I very much understand this frustration. I'm an extreme extrovert, I login to play the game. To use one of the examples, if I logged in to see 8 people active and RPing, even when not with me, I'd feel energized by that place and keep logging in, trying to RP there because 100% of the folks (or close to) are playing! Let's build this thing! If I saw 22 out of 30 people inactive while logged in, and 8 people doing something where I can't join ... then only 27% of the people are playing versus 100%. I'd have more frustration trying to create ideas, entertain and encourage those others who are idling due to all the Nos, not available, regularly happening while trying to get them involved in the game. This is a 'me' problem. But as an extrovert it very much feels like a game is dying and I don't want to waste my time there. That's not always the case, but MU*ing already has a problem of population it is exhausting as an extrovert to feel like 1 of a small group trying to create excitement whether or not I know the same amount of people are playing. Rational vs emotional sides of a being.
It isn't me feeling like I'm special, or that everyone has to RP with me, again I regularly login to play on places with small communities because they 'feel more alive' to me. Overall fewer people may actually be playing but it is certainly easier to identify them. Which translates to a feeling there's a better chance to get involved. And that my efforts to include others get more Yes than No is also great! It's like cold calling the same 8 super enthused customers for whatever you are selling, versus calling 30 everyday and only getting 8 yesses but 22 Nos. For those who have had these sales jobs, the first is nice, the latter is soul crushing - for those of us with that kind of personality - and it's the same end result.
After talking with many more people OOCly who play on MUs I came to the realization, decades ago, that most people on MUs are far more introverted than myself. They don't see activity as inherently energizing they like to feel the connectedness of the online community, and that translates to a safer more comfortable place to relax/chitchat/etc. I will go to a bus stop, a cafe, a night club, etc to do those things. We are using the same space for gaming, but some are also using it as a social connectedness which boggles minds like mine, because if I can't be with you in person it isn't social to me. So I tend to keep my OOC existence out of my game spaces, even when I run D&D/Shadowrun/etc for my IRL friends. It's a work, RL free zone.
I won't say people have to stop idling or not logging in, I get people's desire to have their own way of being. Just know it can turn people away who only have the same desire as those logged in, to make a great game for everyone. This is why I highly enjoy games that have +rp flags, with a separate who for those. It works for both of the people on this topic, gives me a smaller list of active people, and it gives those who idle their space to do so with ability to inform others when they want to play.