1) Melee is at 160 registrants with 18 days left. That's fantastic. History shows that attendance doubles in the last week of registration. I don't think we'll get that here since there were multiple price increases, but nevertheless I expect historic numbers. There will be ~4 new registrants a day for the next two weeks, totalling to ~216 by the final 4 days. Then numbers will boom and we'll see 300+ easy. Maybe even 350+.
It's going to be one of the biggest Melee tournaments of all time. There is no doubt about that.
2) Let's assume round robin pools of 8. If there are 360 people, there'd be 45 pools. For a pool of 8 to run efficiently, it needs 4 setups. So 180 setups in total. With 2 waves, you'd need 92 setups. And with 4 waves, you'd need 48. Now, there will be more than 48 setups (I'd expect ~70?), but what about the three-quarters of the room who's pool isn't currently going on? They'll want friendly setups. And if you use 48 for tournament, ~270 people will be fighting over whatever setups are left.
Compare that with bracket pools, which reduces to a couple setups per pool very quickly.
It's a logistics issue, and though you may not agree, there are reasons behind it. I'm not even sure if I like it, but I understand it at least.