But there are technical reasons too.
When you install AOL, it often installs a proxy cache. After that, even if you change ISPs, every single http request will go through AOL's servers. This will slow down your transmissions. I've people's cable or DSL that works only slightly fatser than modem pseed because of this proxy. The proxy also endanger your privacy.
How do you get rid of this proxy cache? Edit the registry. Best of luck if you aren't IT savvy. Further, AOL tech support will apparently not help you remove the proxy.
The best to deal with AOL is to never use it, or totally re-install Windows from a bare hard drive if you have.
Caches are used to reduce network bandwidth and improve performance. If AOL did not use cache technology for HTML, a large part of the Internet backbone would need to double or triple in size. There is nothing mysterious or nefarious about AOL's use of cache.
...even if you change ISPs, every single http request will go through AOL's servers
If you have proof that AOL forces a former customer's computer signal to route through AOL's own servers even after that customer has switched to a different ISP, I would love to see it. It seems to me that would be grounds for a lucrative class action civil suit, not to mention grounds for AOL's competitors to sue it up the kazoo.