Do folks really typically do that
many practice interviews?
I didn't do any practice interviews intentionally but I did get rejected from the first two places I interviewed out of college, so the effect was the same.
If for some reason a person absolutely couldn't risk being rejected by a few places, practising some other way might be a sensible move :)
The point of a "practice interview" is that you can actually get feedback, as opposed to going and doing a "real" interview for practice.
As for not being able to risk rejection, what is there to risk besides time? I've heard of people practicing for 3+ months. In that same time period, one could probably get 10 onsite interviews and a lot more phone screens in. The fundamental problem is the lack of feedback on rejection (although it's possible to get randomly hired while doing this type of "practice").
As for not being able to risk rejection,
what is there to risk besides time?
Hypothetically, if you interview at employers in preference order, bungling the first two interviews would mean missing out on your first two preferences.
And if you avoided that by applying to your twentieth-preference company first for practice, some people would feel bad or insincere.
If for some reason a person absolutely couldn't risk being rejected by a few places, practising some other way might be a sensible move :)