Lion's Gate is the company that has the rights to the original Ninja Turtles cartoon from 1987-1996, and has been releasing them. They're the same company behind both recent PUNISHER films as well as the Marvel animated DTV's, among other projects. They usually work with low to modest budgets for their projects and can be erratic.
For further confusion, the rights to other Turtle material are all over the place. The NEWER cartoons, from 2003 to present, are distributed by 4Kids, which is part of FUNimation, which is somehow tied to Warner Brothers. The WB also circulated and sold the 2007 "TMNT" movie, and the DVD release of that. Warner Brothers also supposedly has the distribution rights to the 3 original movies, which have been released and re-released individually and in a box set many times.
I haven't bought any of the original Ninja Turtles DVD's. While I worshiped that show as a kid, as an adult it offers little but nostalgia, while the newer series offers that along with more modern expectations of mine. Still, though, I do agree that a saner distribution plan would be good. The problem, though, was that the Ninja Turtle's episode run per season was erratic. The first season in 1987 had five episodes; FIVE. The second in 1988 had a more expected number, 18 episodes. The third season in 1988 had, get this, 44 episodes. Once the show was picked up for syndication by CBS in 1990 (and started airing on Saturday mornings instead of weekdays), the seasons also ranged from 30-40 episodes to as low as 8, the amount of episodes the last seasons had in 1995-1996. Thus, the Season 1 DVD only had 5 episodes because technically, Season One of TMNT in 1987 only HAD 5 episodes (and they added the final 4 episodes from 1996 that didn't air in America as "bonuses"). After that it looks like they started selling 12-13 episodes a collection, until Vol. 4 that had 40 episodes, then going back to collections of 16-18 episodes. I agree, it does seem erratic.
In total, the original Ninja Turtle cartoon had 194 episodes. I suppose the easiest way would be to chop them up as equally as possible, but maybe there are reasons why not doing that isn't done. At the very least, the episodes are readily available; until a few years ago, nearly a decade went by without the series being available in any format.
Granted, it took Disney 11 years to put X-MEN on DVD, and while those are selling like hotcakes (in two weeks, both volumes sold almost a quarter million copies), many fans are bemoaning the lack of any extras of any sort, and even that the video transfer is average at best. I've not bought them but some screen-shots don't look a whole lot better than some of my bootlegs.
Still, it is quite something that in the wake of a 25th anniversary, the TMNT are still on TV, still selling DVD's, and still selling merchandise.