I suppose the staff is trying to sink mesos, but it was great doing single stamp pulls on main characters to try for rare untradables. I can only speak for myself: with no stamps, I'm abstaining completely rather than doing the occasional 50m pull.
The problem is that when we allowed stamps, a vast amount of players changed from spending Mesos to only using stamps, and too many free chairs were being given out. If we allowed this to continue in future chair gachapon events, the prices of tradeable chairs would take a disastrous hit (even the rarer ones). We believe retaining a varied market for chairs as best we can keeps things interesting.
This is the perfect middle ground, keep the stamps for this while only giving tradables with meso pulls. I need that magnus TV chair on everyone...
No, the staffs released the chair gacha to consume too much mesos. I was also surprised that they would issue stamps before, but I believe from their data that after stamps, most ppl will not spend mesos anymore and only do tasks. Turning chairs, I also think it is a bad idea to only draw untradable chairs. If the purpose of chair gacha is consume mesos, we should only use pure mesos to gacha.
TLDR. too many people used stamps so the meso sink wasn't big enough. That's also why you get 20% exp and not drop.