Happened to me many times but just as you, they're not forcing me to do it as it requires some verification of where the funds came. I didn't fill out any of what they're asking for including the IDs because my thought is that I've already provided them some identifications and what's more they need about it? Funds can come from everywhere and it's easy to say that it came from my long term holding and I happen to sell it in some exchanges and transferred it to them for another trade.
You as a user can say it easily but remember an important thing that a centralized exchange is not your own home. It's their centralized exchange's home and they have their own rules which are written in their Terms of Service. They have to obey to KYC and AML regulations from governments so they prioritize defending themselves first, not your account and your fund.
Imagine that if government wants to sue a centralized exchange with Money Laundering Accusation, do you think that the exchange can say similarly like you said and they will have no problems with government after all?
They can not say it and get out of mess created by users on their platforms with deposits from mixers for example. So as a user, make sure you're aware of this fact and be careful with your fund management, its source, UTXOs use for your deposits to any CEX.
I think all of us are aware of it, whenever we use centralized exchanges. We know that they're just having some of their rules based on the government that's implementing it to them. And if the government accuses them of that accusation, the government won't just accuse them without any valid reason or proof. They're more than prepared than us individuals, and don't compare us as individual users to what the government might comply to them because they're bigger than us and we're just typical users and citizens that are free to choose and complain things over them.