Well, the version short version (and IMHO) is that they're different, take time to learn, most people have learned their way around SMAUG and don't have the time or inclination to learn a whole new system, let alone language. For my part I think that dynamic languages are the way of the future for this kind of thing, but I also have already used them for other things and so don't have to pay the initial cost (anymore).
Well, the reason few MUDs use LPC, in my opinion, is that it's a lot harder to just untar the server, configure a port, and say "whoopie, it's a MUD!" At the very least, you need to either find a premade mudlib for your driver or write one yourself – and that right there is more effort than it takes to untar a basic DIKU-derivative MUD.
I'm not putting down DIKU-derivatives one bit. Some of them are quite fun games. It's just that it's a lot easier to put a stock DIKU/SMAUG/MERC/whatever MUD up than to set up an LPC-based MUD.
OTOH, I think LPC-based muds are far superior in many technical ways. For example, with LPC MUDs, you get OLC practically for free, since there's support for object reloading right in the driver.
Might be slightly harder to start, but I think it's well worth it in how easy it is to make things work different than other MUDs. But perhaps people just don't care about making something 'new' anymore, when even the good MUDs are losing players it's probably hard to get the motivation (I don't know any MUD with a growing player base).
People knowing SMAUG better doesn't seem like much of a reason, people could just start with LPC instead!
Ease of use. It's as simple as that. Today's admins just want something they can download, compile, run. They typically want OLC that gives them the fastest route to finished good, if they're bothering to even do that much. I've not run into one LPC based setup that you can do that with, and they all seem to expect their builders to really be coders.
It's also the same reason there's such high resistance to implementing things like Lua in Diku based systems. Lua and other things added properly would blur the lines considerably between Dikus and LPs.
Also, yes there are loyal LPC users that think it's the best thing since sliced bread, but I can also honestly say I've seen several builders on TBA that have built on LPC before and have said they HUGELY prefer the OLC of tbaMUD to the near-coding required to do the same on most LPC muds.
I'm also not sure I'd say most people are used to smaug. I think honestly there's more muds using ROM or one of its codebases than the smaug derivatives (not on this forum, but in general). There probably are more smaug than circle though, though we're abundant as well, just not on these forums. Not sure if it's much of an indicator of actual # of users for each codebase, but smaugmuds.org only has 421 members whereas cwg.lazuras.org (the largest circlemud forum) has 1170 members.
The smaug community in general is pretty fractured and you'll find there's probably a lot more than those who show up here and over at smaugmuds.org. Nick Gammon's site has lots of them that barely know the rest of us exist. It may just be that with tbamud.com that you've managed to consolidate more of them in one place. Does your figure also factor out spam bots? We have none of those as far as I know.
Yep, possible that say 5-10 could be spam bots, but generally there's very few and when there are their deleted so if any are bots it's a very small minority. I myself admitted before and still do that the number of users on the sites may not at all be representative of the number of users of their respective codebases. I was curious so I also did a search for each codebase on TMC:
Circle: 142 Smaug: 73 SWR: 30
I think that's the only 2 codebases listed on TMC that are smaug or smaug derived, but not 100% sure. (I'm not saying that more circle muds listed on TMC necessarily means there are more circlemuds than smaug either, so much as just that the numbers might be a lot closer than most people here would think due to the majority of the users 'here' using smaug.