Especially since the video is blocked by the NFL.

You have to control the ball to the ground. See the Pittsburgh game on Sunday.

Item 1. Player Going to the Ground. A player is considered to be going to the ground if he does not remain upright long enough to demonstrate that he is clearly a runner. If a player goes to the ground in the act of catching a pass (with or without contact by an opponent), he must maintain control of the ball until after his initial contact with the ground, whether in the field of play or the end zone. If he loses control of the ball, and the ball touches the ground before he regains control, the pass is incomplete. If he regains control prior to the ball touching the ground, the pass is complete.

In this case, the reception is made and he touches his feet in bounds-touchdown at that point. If instead it was a diving catch it should be ruled incomplete. The difference is he scored BEFORE falling down

you have to control the ball all the way to the ground.

Here's the video from YouTube. At the very end of the video, it shows that the receiver, who did get both feet down in-bounds, didn't control the ball all the way to the ground as the ball hit the ground first when he came down. Neither his hand nor an arm was under the ball so it shouldn't have been ruled a catch.

But as I commented on another thread today about the nullified Steelers' touchdown catch from yesterday's game, the NFL always rules for the Pats in murky rules situations in games — just as they did in the most famous, err ahh, infamous one of all — the Tuck Rule game against the Raiders years ago.

Take a look at the last few seconds of the video:

The difference was that in Sunday's game the player was going to the ground. In the OP's example the receiver catches and makes a toe-tap to score a touchdown prior to falling. Different situation and different rules.

He completes the pass for the td and then falls

You have to complete the catch through the ground.

I will give you a clip and a link:

A forward pass is complete (by the offense) or intercepted (by the defense) if a player executes a three-step process:

secures control of the ball in his hands or arms prior to the ball touching the ground;
and touches the ground inbounds with both feet or with any part of his body other than his hands;
and maintains control of the ball after (a) and (b) have been fulfilled, until he has clearly become a runner (see 3-2-7 Item 2).
An additional item makes it clear that if a receiver is going to the ground in the act of completing a catch, he must maintain possession even after he has gone to the ground. This isn't a separate rule, as some have painted it. On the contrary, it makes clear that even when going to the ground the receiver must possess the ball for a period of time.

Simple. Want to complete a catch? Maintain possession and become a runner, or maintain possession through the process of going to the ground. Simple.

https://www.sbnation.com/nfl/2015/12/9/9867846/nfl-catch-rule-smart-explained

Exactly. Cooks did not "maintain possession through the process of going to the ground" As he went to the ground, he lost control of the ball.

The receiver still has to control the ball to complete the catch.

Dispute it all you want but that player didn't.

NFL always rules for the Pats.

is the logic that they always rule for the Panthers?

I week earlier, with the top team in the NFC at that point, they ruled exactly the same way and that would have likely resulted in the Vikings beating the Panthers. Nobody lost their shit then and claimed the refs always favor the Panthers. Just because this EXACT SAME CALL was made and it involved the Patriots doesn't mean they favor the Patriots. It means they have a shitty rule they need to revisit.

the rulebook before anyone noticed. It wasn't like it was put into the rulebook in 1999, and certainly it wasn't used AGAINST the Patriots in week 2 of that very same season when Vinny Testaverde's Jets had the same thing happen to him and the Jets got to keep the ball.

In the Steelers game Jesse James did not go to the ground in the act of catching the pass. He caught the pass, went to his knees, turned and reached the ball across the goal line, and went to the ground as a result of reaching the ball across the goal line. Whether or not the ball "survived contact with the ground" was utterly irrelevant.

the one from the OP should've have been a TD as the ball hit the ground first without a hand or arm underneath it.

Different rules for the Pats though.

A player who makes a catch may advance the ball. A forward pass is complete (by the offense) or intercepted (by the defense) if a player, who is inbounds:

secures control of the ball in his hands or arms prior to the ball touching the ground; and
touches the ground inbounds with both feet or with any part of his body other than his hands; and
maintains control of the ball after (a) and (b) have been fulfilled, until he has the ball long enough to clearly become a runner. A player has the ball long enough to become a runner when, after his second foot is on the ground, he is capable of avoiding or warding off impending contact of an opponent, tucking the ball away, turning up field, or taking additional steps (see 3-2-7-Item 2).

On your knees you are going to the ground because you cannot clearly become a runner. He could have covered the ball and been secure on the half yard line but instead reached across the goal line continued to the ground and failed to control the ball

But it's the Pats so it's a touchdown.

I missed that the first 6 times I watched it.