What's this establishing-a-player-base? Do you, as GM, curate a game group? Do you, as a player, play D&D just long enough to find other players who match or complement your playing style?
I regularly invite people to play TRPGs, but I don't use D&D as the gateway. The system we use depends on circumstances. I often recruit people who are new to RPGs; teaching them D&D is no easier than
DFRPG (for example), so I usually start with what I prefer. They've usually
heard of D&D, of course, so it helps somewhat that I'll be using the same heroic fantasy genre. (One of the reasons I dropped D&D as my preferred system was because new players kept asking to play character concepts that didn't exist and were hard to build without a toolbox system like GURPS.) I do run and play D&D games sometimes, but that's usually with established groups (i.e., jumping in to DM a side quest), or because we want to run a published adventure without bothering to convert it. Contrary to what I hear on the forums a lot, most gamers that I know are open to trying other games as players. GMing a new system is a different matter because it requires such an investment of time (and money), but most are happy to try any game that someone else volunteers to run.
Have you been told that you're not welcome in a group? Or worse, have you been told that a group was disbanding, just to find them playing another session without you?
I've never been explicitly booted, but I've certainly walked away from groups where the chemistry didn't feel right (and I may have been on track to be dis-invited eventually). In my own games, over many years, I think I've explicitly removed three players. All of these were due to critical differences in play style, genre expectations, etc. Interestingly, I continued playing with all three people in other contexts (i.e., them GMing, different genres, entirely different groups, etc.) and they were great. They just weren't a good fit in my long-running campaigns and were causing other players a lot of grief.