I'd ask why they don't make it optional (I'm not a Brave user) but it seems it was.

Another issue is that Strict mode is used by roughly 0.5% of Brave's users, with the rest using the default setting, which is the Standard mode.

This low percentage actually makes these users more vulnerable to fingerprinting despite them using the more aggressive blocker, because they constitute a discernible subset of users standing out from the rest.

Given that, I'm inclined to agree with the decision to remove it. Pick your battles and live to fight another day.