>>156941038Even thinking a little could give you this answer.
1. He's scared shitless of Beerus and will agree
2. It's better than being stuck on a tree getting sung to by flying babies all the time
3. He at least has a CHANCE of escaping which is better than none at all
It could be any one of these or maybe multiple. I really don't get why it's so hard for people to see why Freeza would agree. He's obviously going to have ulterior motives and not going to be all happy go lucky and friendly to save the universe. There's a 100% chance there will be some form of confrontation between Freeza and Goku during the tournament.