I love mods and modders! I'm consistently impressed by both their talent and dedication to the game. I love seeing the creations, and have even enjoyed many of the videos showing how it's done (even though it's well beyond my ability level to do or even follow, it's still fun to watch).
Unfortunately, I'm not very technologically advanced, so I did not use mods back when only replacement mods were available, because I worried that user error on my part would lead to problems that I might not be able to figure out myself. (I want to emphasize that this is all about user error by me -- not the mods or modders themselves).
I also play mostly in franchise mode, and really enjoy the trading/welfare/breeding/management/challenges parts of the game. Since the animal mods can't be used in franchise, there is a portion of the enjoyment that is missing for me, in much the same way that some players don't get as much enjoyment from exhibit animals because they can't do the things with them that they most enjoy doing. This, again, is in no way the fault of mods or modders. Just a technical limitation that places them largely outside the possibilities of my preferred game mode.
That said, when non-replacement animal mods came out, I downloaded every one of them and created a sandbox zoo (MOD-ern zoo) that had habitats for every single non-replacement modded animal. The non-replacement mods were within my technical comfort level to install, didn't replace my franchise options, and I loved having so many new animals to choose from, since animals are the main reason I play the game. It was heaven!
A huge part of my comfort level at that time was in the hope/speculation that they might not break with future updates. When that didn't pan out, my personal use changed. Again -- this is in no way the fault of the mods or modders, who have been amazingly awesome about upgrading things following each new dlc/update, and amazingly helpful and transparent about what is happening and how to prepare for it ahead of time and fix it afterward. But for me, the fear of personal user error in getting them in and out every three months, the fact that I couldn't place them in franchise, and the correlation with things beginning to re-open in my area after covid, with all of the events and responsibilities that entailed, meant that my time to play the game decreased and I've had to choose how to use that time. I decided that faced with the maintenance time involved to be able to play in only my less enjoyed modes, and the worry that I might forget and miss an update that might make a zoo unusable and lose much of my work, that it made more sense for me to spend my gaming time working on my franchise zoos, and let the mods go by for now.
But again, I think the mods and modders are great, and I fully anticipate using them quite extensively in the (hopefully distant) future when dlc support stops and/or if franchise mode winds down (whether officially or just through fewer trading partners). I could also see myself giving them a try before that if the technology developed such that mods were usable in franchise mode, or if there was a commitment by frontier that they wouldn't break with future updates. (Although I understand neither of these possibilities are likely to happen).
At a larger scale, I do worry about the fact that mods can't be used in franchise mode, what this means for the game as a whole, and whether I'll be left behind. Again, I don't think this is the fault of mods or modders -- They would happily make their mods available to everyone in all modes if they could. But there are already existing chasms between play styles and game modes, and those chasms widen as more things become possible, normalized, standard, expected, or assumed in one part of the community, that aren't in another (and that goes in all directions). While there are lot of players who play across modes and across settings, I think the unavailability of mods in franchise (which again, is not the fault of modders), does have an impact that effects all of our other discussions in various indirect ways -- often subtly, invisibly, tangentially, or cumulatively. It starts to show up in all the other conversations, from the relative importance of animal welfare in franchise success to the lack of high genetics in sandbox, from the number of animals available in one's vanilla game mode (I personally prefer the kink of trading!), to larger questions about how many and what kind of dlc are needed, to which workshop items can be used depending upon one's modded building options. Mods and modders aren't responsible for this expanding list of differences (and shouldn't be expected to do anything differently because of it). But it is another place where our worlds diverge, and our needs and possibilities become less recognizable to each other.
But never fear -- Ten years from now when they stop making DLC, I'll be first in line to get every mod there is, just as I was when the non-replacement mods first appeared.