Personally, I think that, for the few, and it's my belief it's only one or
two in our galaxy, intelligent species that have interstellar travel
capabilities, they probably do follow something like the prime directive.
I think what you have to realize is that such a "directive" is impossible. Alien societies are probably even more complex than ours, with huge
chunks of the population probably having access to interstellar travel. I don't think it would be possible to uniformly enforce such a policy
forbidding contact with undeveloped worlds.

You assume that interstellar spaceships would be as common as cars,
which is highly unlikely.
Apart from that, who's to say they would come here?
Think about it, people don't generally go onto restricted property
unless they are allowed.
Or it could be to that there psychology is very different than ours,
and such a notion a prime directive like idea is ingrained into them.