Complementing Alexander's answer, a close reason of "lack of research effort" is, in my opinion, intrinsically bad for multiple reasons: it is impossible to ascertain how much research effort there was, "effort" is not a cop out for a poor question, it often gets dragged down to debates about how often students have "no clue on where to start" etc. If anything, "effort" is frequently a red herring or simply a compromise for allowing bad questions to stay.
It seems to me one of the primary reasons people have for closing is lack of research effort (...)
I'd contest that. I realize that a lot of people that close a lot of questions may even agree with you about it, but I don't think this is true. If a question such as:
calculate derivative of 1/x. Please help.
was attached with an eight-hour long video of OP studying Stewart's Calculus book, the question would also be closed. What matters most for people is that the question, as written, is not relevant to the community. And this is explicitly said in the close reason. Of course, it has a personal undertone, as does any kind of intellectual quality curation. But the solutions for that are rather objective and are also within the close reason itself, and it seems fair to say that the overwhelming majority of questions which follow those guidelines are welcome here and left untouched by closure.
It also seems to me that "[please, show the] background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." is much clearer and objective than "please, show research effort" or variations of that. A new user of the site, when confronted with the later, may simply respond by saying "I tried using the definition, but then got stuck" or variations of that. Indeed, this has happened multiple times. The phrasing of the close reason makes it so that what may be important about effort (namely, the background, possible strategies etc) are spelled out explicitly.