Seize the Initiative

So, I've had a question on my mind for a little while now and I am wondering if anyone can help clear it up. The current 8e seize the initiative rules, combined with how deployment and deciding who takes the first turn rules...

As far as I understand it, the basic gist is there is a roll off that determines who starts setting up first and each player then deploys one unit at a time. After chapter approved the suggested rule (that as far as I know like 99.9% of players follow) is the first player to finish setting up gets a +1 to their roll in a roll off to determine who is going first.

And then whoever is going second immediately rolls to see if they seize. It made sense when you knew who was going first before deployment ended. So assuming I have all of this information correct, my question is: Why? Why have a seize the initiative roll with the roll off after deployment? I understood it in previous editions, even if it was the most nerve racking roll of the whole game. You assume to know who's taking first turn, then both players set up, and THEN a roll is made to see if there is an upset in the previously assumed turn order.

But with two rolls happening right after one another, it seems like a pointless waste of rolling a die. You are already deploying not knowing who's going first, so what is there to actually gain other than two dice rolls rather than past editions chance to disrupt the assumed order of the game?

If anyone can shed some insight on this, thank you.

You're not wrong.

Initially as the rules dropped you knew who would go first based on who had most drops, with some variation with players maybe deciding to deploy outside transports and suchlike. At that stage the seize roll generally makes sense.

Since that seemed overly in favour of certain types of armies, Chapter Approved had its suggested change of a +1 on a roll off instead of an automatic advantage to the smaller number of drops.

As a result we have back to back rolls where a single one could do. There is some complexity with command rerolls, but ultimately they could simplify it to less drops on a 3+ and the whole process could be simplified.