Is there any reason not to enable all the blocklists and filters in uBlock Origin that aren't enabled by default?
And why aren't they enabled by default?
Finally, are there any other quick/easy things that can be done by users to improve uBlock's blocking... like maybe installing some other blocklists that aren't in uBlock Origin at all?
The primary reason for not enabling every list is that some additional % of sites will "break" (although frequently, this will only be cosmetic).
An example of this is that the lists can block very general class or id attribute such as #cookie-banner. While it's likely that you'll want this blocked in general, some small number of sites may have an element (unfortunately) named this that is functional and that you actually want to see.
Because some of the lists have tens of thousands of entries, these edge cases can add up to break more sites than is actually desired. So there is a give/take there.
Another point is that some of the lists are redundant but have different maintainers. So it may make sense to choose one of these, but you it would just be additional overhead to check them all.
In my experience, running the default lists along with the "Fanboy's Annoyance" list and a few custom entries in "My filters" provides a good experience for me.
And why aren't they enabled by default?
Finally, are there any other quick/easy things that can be done by users to improve uBlock's blocking... like maybe installing some other blocklists that aren't in uBlock Origin at all?