ICOs did not in anyway affect exchange platforms, if you windback on the years, icos were very prominent in the year 2015-2016 during the early years of altcoins. Since then, icos have evolved from ico (initial coin offering) to ieo (initial exchange offering) to ido (initial dex offering) and so on. None of this have affected exchange platform because after every successful ido/ieo/ico event; these tokens end up listing on exchange platforms.

I think the major factor that affected market of exchanges is overcrowding; there are too many exchange platform in the space today with many redundant and without volume.