Please..

If you pay for it.

Is FTB not primarily meant for managing and integrating mods?

From what I understand, Minetown specifically uses server add-ons/plug-ins which implement server functionalities required for moderation as well as other things such as the MTC currency system, donation perks, automated announcements, petition/helpticket system, home teleport system, land claim and container protection systems as well as other things.

Minetown is for the most part a Vanilla server, the general minecraft experience is not modded. All clients require to log in and play is the standard launcher that comes with the game and a currently supported version of the game. FTB servers require that the clients also have a FTB client with the servers array of mods in order to connect and play, which filters out players. While the modding community is large there is likely a much larger number of users that don't use mods. Minetown simply isn't made for FTB and it's plug-ins probably aren't supported by the FTB launcher(yet?).

If you are suggesting they create a separate server with mods, what mods would those be? Who chooses? The current owners and staff? How many mods is too much? Many players don't have particularly powerful computers that can handle a boatload of mods. There is a lot to consider.

There are many heavily modded servers out there that out compete Minetown by a longshot, most notably due to Youtube exposure by "Letsplayers" that are either actual staff of those servers or fans of those particular servers all with a particularly large number of followers/viewers whom actively participate with them on their servers. Minetown would need to become very active once again to make this worthwhile, I imagine. The particularily great aspect of Server dependent plug-ins is that the clients connecting do not need to download and install anything special in order to use the custom functionalities and mechanics not seen in a vanilla server, which makes the server accessible to as many potential players as possible.

The problem with making a FTB server isn't even cost, sever hosting fairly cheap. It's the time and effort required to make make and maintain one. It's heavily modded which bogs you down with extra labor from the start, but in addition to the setup there's so many extra things that can break and way more ways to cheat. it also requires someone familiar with the mods and how they can be used to dupe/grief so they can negate those items that can be used for Evil. Most FTB servers are short lived for a reason.

Hit the nail on the head. The infrastructure exists for such servers, but the scope of the playerbase is very limited in contrast to the current playerbase of the community, and just doesn't provide a good return on the time and work invested when it's done on a public platform. That being said, there are plenty of communities out there that do specialize in modded servers, where it's been their bread and butter for years. The infrastructure that's been built into the FTB community as a whole has gotten better over the past few years, so you would likely be able to find any number of good FTB servers out there that would fit your needs while AfterEffect, Everrius, and the rest of the active staff seem to be doing a very good job at holding down the fort here.