In short: people will attach stuff to bitcoin and we there is NO WAY for us to stop it.

They can do it in many different ways, and some of them are more harmful.

Using OP_RETURN for this purpose is less harmful for the network and noderunners than other methods, because it does not bloat UTXO set and has no validation cost.

But OP_RETURN has a limit which is too low for some of those protocols, so they need to use less efficient methods that increase the cost for everyone and do more harm.

Hence the idea to relax or remove the limit, to incentivise them to use less harmful method