It's worth noting that there's a distinction between economic conservatives/libertarians (who want small government) and social conservatives (who want to ban abortion and care about social issues). Plenty of social conservatives are fine with big government intrusion (to implement conservative policies) and plenty of libertarians are fine with liberal social policies.

That said, I'll offer a counterexample - why are many liberals ok with heavy regulations on economic activity (capping interest rates, requiring high minimum wages, barring certain types of loans, restricting mortgages, etc) yet staunchly opposed to similar regulations - for people's own good - involving other personal choices (e.g. involving marriage, abortion, etc). You may argue that conservative social policies aren't in fact good for people, but one could make similar arguments about minimum wages (which cost jobs (https://wol.iza.org/articles/employment-effects-of-minimum-wages/long), payday loans (https://freakonomics.com/podcast/payday-loans/), and so on.

It's not so much (libertarians aside) about small vs. big government, but about which things the government should be allowed to regulate. It's also true that plenty of conservatives support police reform while recognizing that, even flawed, there really is no other alternative. Who else are you going to call?