Maybe they don't see them as bad-looking. Men all like different types of women. Some like ones that are a bit meatier, some like ones with smaller breasts, some like ones that are short... Regardless of societal standards of beauty, people are going to have their own preferences.
That being said, men in the sorts of relationships that you mentioned could be trying to avoid an actual relationship. Perhaps they just want someone to be with (either to quench their loneliness or sexual urges). Perhaps, to them, having a not-so-great girlfriend is better than no girlfriend at all. I heard someone suggest that some people are in relationships because they fear solitude.
It's also possible that these women have beauty that you just aren't seeing.
Yet, if it is the case that these men pursue doting women, consider this: who doesn't like to be worshipped? Maybe they like to feel like there's someone who cares about them or maybe they just like being doted on because it's flattering. The relationship may not be enriching, but some people would gladly take attention and complete and total devotion over an enriching, meaningful relationship. Again, maybe having an actual relationship isn't a priority to them.