How is student loan debt crippling to some people?

I'm applying for university this year and have sorted out my student finance and such. I understand that debt is repaid back if you exceed a salary threshold of £25,000, in which you pay 9% of your salary. I also understand that I'm most likely not going to pay it back until in my lifetime. That being said, I genuinely can't see how student loan debt can have a massive negative impact on someone.

I saw something about a graduate refusing to apply for jobs that pay over £25,000 because they didn't want to make any repayments, but this seems incredibly dumb to me. Why would you cap yourself at under £25,000 when you have clear opportunities to earn way more? I've seen people say that they don't notice the money leave their account since it's like any other tax.

I've seen somewhere that it could affect your ability to take out a mortgage on your house or something, but I haven't really looked further into that. My aunt has £184,000 in debt and has a house plus three kids, so I'm assuming it isn't that much of a detrimental factor. Obviously times were different since she went to university, but I feel like the point still stands.

If someone could explain it to me, that would be appreciated.