I have purchased old Macs and new Macs. In fact I can almost guarantee that I own more old Macs than 98% of the forum members here.I think it's all a matter of price and priority. Some people (me included) continue to use their Macs well past software support. Some stay years without updating their updatable Mac (I only updated yesterday my M1 from Monterey to Sequoia and I am not planning to update to Tahoe, I will see what come next). Yes, I don't care about security patches, I have never had issues and I am totally ok with taking what I consider a moderate risk (my main machine is a Windows 11 computer however).
The advantage of old machines are that they can be really cheap, which is why I may get them for secondary machines. However, these days I won’t use one as my primary machine, just like you aren’t using one as your primary machine.