I did my undergrad and graduate degrees in the 90s, and it's worthwhile comparing to the situation then. The internet did exist (email, usenet, and -- gasp -- browsers!) but indexing and search were poor.
In more technical subjects, we got assignments we were supposed to figure out on our own, to test and expand our knowledge of the material. Yes, sometimes someone found a worked solution to the question, and saved some time copying it versus figuring it out on their own. But hunting through sources in the library was educational on its own, and by hand-copying out the solution you couldn't but help internalize it, learn from it, and generally write it in your own words a bit. So educational objective realized, if perhaps suboptimally.
In less technical subjects, when we wrote papers the expectation was to research, and then articulate in our own words. Once again, absent the shortcut of Google search-Copy-Paste, mindless copying was less of an issue. Did students sometimes plagiarize? Of course, but the extent of it, and the impact of it on their understanding, was much less.
"Cheating" did happen, of course, on assignments, and sometimes even by "buying" papers. But professors who found that an issue modified their assignments over time so it became less attractive and easier to detect.
While the situation of course varies from case to case, today's frequent student plagiarism comes from a pernicious assumption that Search is an alternative to actually thinking about a problem, rather than actually engaging with it. By and large, correctly detected plagiarism (and there can be errors!) does not penalize students who "thoroughly researched" the topic; it catches those who searched-copied-pasted in lieu of researching -- and often haven't yet realized that research goes beyond search!
Finally, to your point about "not everyone wants to do research". That is true, and I've since also managed teams doing applied R&D in industry so I'll bring that perspective as well. When a team member says, "I've found this interesting approach to our problem on the internet, and here is why it's relevant, here is how it's different, and therefore here's what we should think about before using or adapting it", that is super valuable. However, "Here, I've solved our problem! [And it looks like I did something impressive, but I actually just found something on the internet and hit Copy-Paste]" is not, primarily since it's much likelier that person cut corners assessing if it applied well, thinking through complexities that might be missed -- as well as might have swept under the carpet IP (intellectual property) issues that might be significant.
"Plagiarism" on school assignments is more like the latter than the former.