Because it isn't fun checking if the whitespace at the beginning of the line is a tab or spaces. And as said, you must know when to use tabs and/or spaces in rules.

For doing such a simple thing as calling some commands, Make has way too many subtle footguns which _will_ bite somebody, someday. The problem (that's not a problém at all, that's a reason to celebrate!) is that most JS devs and users aren't used to Make, compared to e.g. C programmers. To rephrase: as someone writing C, you have to use something like a Makefile, as anything else (like scripts) gets unreadable and -usable quite fast. But if you can get away with a less complex solution, you should really use that instead of Make.

that's why https://editorconfig.org/ exists, so that neither you nor your teammates have to think about these things

You're better off using a Makefile linter. But you must know about the problem before being able to solve it. And error messages like

   Makefile:2: *** missing separator.  Stop.

Is that Stockholm syndrome? Or an appeal to history/authority in action? What makes people believe that this is even remotely reasonable.

inb kids these days, I started in the '90s and wrote my share of makefiles. Tolerating make only made sense until 2010-ish, then both hw and sw advances rendered it useless.

Edit: just realized my reply to a wrong person, but let it stay here