Why don’t native English speakers use this phrase “Could I ~? (ex)Could I help you?”

I know that they use “May I ~?” or “Can I ~?” instead of “Could I ~?”

Please tell me the reasons.

See a translation

Oh that's a really good question! mm there's probably a better answer but I think it's because 'could' implies both future tense and uncertainty.
for example, when you go to a hotel at the reception desk they would say:
Can I help you find your room? OR May/Can I help you with anything?
The employee would say can because they really CAN do the thing, they are able to help.
Or they would use may to say 'I can help you and I am politely offering my ability to".
Could I help you? sounds unnatural because it means something different. for example:
- I'm having a hard time with this problem...
- Oh it looks complicated... could I even help you?
- I don't think so because you've never taken this class..
With could you are asking the person who needs help if you, the helper, has the ability to help, which is... kind of weird.
more explanations welcome!