I think any accountant and lawyer does this to some extent, if I'm honest.

There's no obligation to take on any client. If a client has a problem to be solved but very little money, of course we're reluctant to get involved. If it's a situation where a potential solution is "you should call the tax office and tell them XYZ." then that's really just a polite way of telling them you don't want to get involved.

Lawyers will work in a similar way, but are more likely to truncate their advice to "You should call and ask them what to do".

I've often heard of lawyers explaining to potential clients that the costs in pursuing their matter would be unreasonable given the likelihood of success.

It's not really altruism, although I'd like to think that I do my best to help people when I can. It's really just a natural way of avoiding doing a heap of work for someone who can't afford to pay you. Additionally, if you can make the client feel like you've helped them instead of just rejecting them then they will be more likely to recommend you to their friends and family who may be a better fit.