I am a toy collector... not a marketing expert. Maybe all my thoughts on the topic are BS, I'm not sure.
Currently most toys are released in Waves. Most stores seem to order a couple of cases of each wave. Sometimes they all go out on the shelves at once and other times the first case goes out and once they sell the store restocks. That wave may be readily available for a couple of months and then they are gone. Short of a really bad peg warmer hanging out forever.You better get the figure while the getting is good.
When I was a kid in the 80's and 90's toys were released for a year. So for a year or a little more you could easily get any character. I would make my Christmas list and if I didn't get the guy then I could ask for him again for my Birthday in May. If you were lucky stores would misplace cases and dig them out later making figures from the previous year available again.
Using the year system meant that main characters like He-Man, Snake-Eyes, the Ninja Turtles, and Batman might get a new variant once a year or so. Now some of these characters get a new costume or version every wave. Why is that?
Collectors don't necessarily want all these different versions, but the toy companies say that these are for the kids. Kids want the main characters so in order to get new kids into the line they have to always have a Batman or He-Man on the shelves. I feel like this tends to cause the most peg warmers. The old system instead of having 4 different Cobra Commanders released in one year, the same one was available all year. The shorter length of release for the waves is good and bad for collectors. It helps the collector market by making figures gain value because once they are gone they are gone. It also makes collectors pull their hair out if they can't find the figures.
When the new Nick TMNT figures came out I bought a set of all the figures to play with (make an animated video) but I also bought a set of the 4 turtles and a Shredder to keep packaged. I have they stored away in a closet and when I retire in 20+ years I'll see if there is a collectors market for them when the little kids of today have grown up. I don't think I'll get rich off them, but if I double my money later that would be fun. I occasionally buy a few figures to resell down the road from hot toy lines. I assumed that once the turtles were gone they would be gone, but the stores have been restocking them. I see the regular Turtles alongside the variation Turtles with the ooze gimmick all the time. April, Splinter, and Kraang seem to be the rare figures from the first wave.
In the 80's and 90's they used to reissue figures from time to time. Masters of the Universe is famous for including the little "Original" bursts on the front of their reissued figures. Mattel even carried on that packaging gimmick with their modern figures. Again making older figures available to new fans.
In the 80's and 90's toy lines were also supported with comics, cartoons, and commercials. The only toy line that is currently being supported properly in my eyes in the Nickelodeon Ninja Turtles. They have all three. It's been over 10 years since I've seen a GI Joe toy commercial. There are several GI Joe comic books released each month, but none of them feature the toys that are currently on the market. Maybe that is a good thing... but I think a comic geared more towards the kids could also be good.
The 80's GI Joe comics by Larry Hama were fun for people of all ages. They featured both old and current products. I was never upset that I couldn't buy all the figures in the comics. I understood that some figures were older and no longer available. I used to hunt for those characters at yard sales. Maybe that is what turned me into a toy collector.
The stores also have a lot to do with the marketing and I don't know if that good or bad. We see store exclusives from time to time. There are also stories about figures like Kwinn and Data-Viper (from GI Joe) who got squashed because the retailers don't like them.
Action figures are getting to be more and more expensive and if they
aren't supported and marketed properly I worry about the selection in
the future. The toy companies tell the collectors all the time that they
are a small percentage of the total sales and the kids are the driving
force. The collectors know what is available and actively seek out the new products. How are toy companies tell kids what's out there?