Hi @wellbing-go 
Mmh an interesting one… Although I’d say users don’t read (I’m guilty of this too) in general, I’ve not had issues with other users choosing the wrong category unless they are new etc.
Are your category names short and obvious? For example Support. And is the category description written well?
I’d try and find out why maybe its just the users or perhaps its confusing. Reach out to them via PM or create a topic explaining that categories are there to help organise the forum and increase its searchability etc. So it helps everyone if topics are categorised properly and if they have any questions to contact staff.
These are just my ideas but I’d love to hear what other ideas / experiences others have here.