Because each university has university-wide rules forbidding sharing assignment solutions. It is explicitly forbidden even before starting the course unless the syllabus or professor directs you so. You can't "help" others on their own assignments by giving your solution. You can't receive direct "help" either.

Edit: here's the text of my alma mater: Any behavior of individual students by which they make it impossible or attempt to make it impossible to make a correct judgment about the knowledge, insight and/or skills of themselves or of other students, in whole or in part, is considered an irregularity that may give rise to an adjusted sanction.

A special form of such irregularity is plagiarism, i.e. the copying without adequate source reference of the work (ideas, texts, structures, designs, images, plans, codes, ...) of others or of previous work of one's own, in an identical manner. or in slightly modified form.

[https://www.kuleuven.be/onderwijs/oer/2021/?faculteit=500004... translated with Google]

In my time in college I helped a lot of fellow students work through a lot of assignments. I sat down with them and helped them to think through the problem and find examples to learn from that weren't full solutions to the assignment. I helped them find difficult bugs in their implementation by pointing them in the right direction or showing them debugging tricks I found helpful.

What I didn't do was show them my implementation or even talk about how I solved it. Yeah, doing it the long way takes a bit more effort, but the result is that the students I helped actually understood the code they submitted and were better equipped to solve the next assignment without help.