there is a risk that game will continue for 350 moves
even if you make all moves instantly, opponent may use time 100%
so, 30s * 175 = 5 250 seconds
its 87 mins
so such game may take 1.5 hours without main time
with 30 minutes main time it becomes 2 hours
if you need time to think, it may be 3 hours+
so, accepting anything with main time more than 20 mins and byo-yomi more than 30s is dangerous
its not surprising that people prefer faster.
30s without main time may already be too much sometimes.