Some good suggestions being given here. But for slightly less dependency on a particular set of neighbors and broiled frogs, I have a few other things to offer.
1 - There are two ways to enjoy more of the EP and store set collections of fun you already have without having to keep moving worlds and stop/starting gameplay.
a - One is to use Edit Town to put a cross-section of fun types lots from what you have to work with into one world. Most of my worlds have bowling alleys and dance clubs, for example, there is no reason why Uni World and Bridgeport need to have a monopoly on those. But don't get carried away because, as has already been noted, too many fun community lots in the same world will lead to sims available to visit them being spread out too thin.
b - If not averse to using mods, have your sims vacation to the other EA and maybe custom worlds you have available by way of NRaas Traveler. That way if they live in a colder urban setting or a more mundane suburban one, for example, they can still enjoy tropical activities, resorts, casinos, mingling with a mostly occult population, horeseback riding, etc. by vacationing in worlds that offer these more naturally and not be limited to the 3 WA worlds, Uni, and Oasis for destinations and fun places to make new friends while taking a break from the typical work-eat-sleep-skill up grinds.
2 - In addition to too many community lots vs. the local population (this is more evident in Bridgeport than anywhere else), there is also a possible technical reason for the empty lot syndrome. If your processor or graphics card is under-powered or, just as much, if the game thinks they are even mistakenly, it will throttle sending sims out to community lots in a sometimes misguided effort to preserve performance. If the game is unnecessarily under-ranking your components, this can be fixed with some simple edits to the base game's sgr files. The DeviceConfig.log, a file that gets generated on each startup of the game and is in your TS3 user game folder in Documents, if you care to share the first 40 lines or so (not the long lists of game options that follow) would tell us if this is part of what is happening -- you could send it by way of PM if you prefer not to paste it in here.
Of course, if your system really is under-powered for the game, then the community lot throttling is supposed to happen for a good reason and it shouldn't be overridden. The DeviceConfig log would tell us that as well.
3 - If you are not happy with the way in which EA's built-in story progression is managing the inactive residents living in your worlds, you may want to try a modded version to see if those do more of what you had in mind. The two other choices are NRaas StoryProgression and AwesomeMod's StoryMode. They both work very hard, and in very different ways, to keep demographics in balance and help to prevent the Ghost Town Syndrome and worlds full of elders who never bothered to have kids along the way to keep the population going. Uni World is a special case, although NRaas SP can help there too with a bit of work on the part of the player should they wish to periodically repopulate it with fresh student bodies.