Some points to ponder:
>??> As most of you know, a fielding glove is sewn together inside out, then inverted before inserting the liner. Maybe since Horween tan is so stiff, the factory must skive the glove pieces thinner to make the glove pliable so it can be manufactured. This makes the Horween leather glove softer.
>??> Maybe gloves like catcher's mitts and first base mitts that don't need to be turned inside out after shell assembly don't need to be skived thinner, so they use more full thickness leather pieces in their construction, thus feeling "thicker" or "stiffer."
Also consider this:
Depending on the season in which a glove is produced also makes a difference in the stiffness of the glove. Gloves produced in winter (at least in more northern climes like China's Shanghai area, Japan's Nara prefecture, etc.) are stiffer than gloves made in summer. Moving production to warmer climes like Indonesia, Vietnam, or the Philippines has been a way for brands to reduce the chances of this happening.
It's more to it than just the points you've made. Cattle just isn't raised the same way it was 50, 60 years ago. Just as not much free range cattle that's allowed to reach full maturity as there used to be. Free range cattle that's allowed to reach full maturity will produce thlcker, tougher hide. That's what code 55 Horween used to be produced from! Of course the leather back then had a lot more natural imperfections because of the natural way the cattle was raised. No pens or enclosed spaces. No special feed or food additives.
Nowadays, most people (even on this board!) want visual perfection. Gloves get sent back for a nick, a discoloration or for whatever like it's not going to be used outdoors in dirt, rocks, grass & sometimes rain to catch a projectile hurtling at you at 100mph. I never understood that.
Another issue is that now everybody primarily buys things on-line. When I was coming up, there was no, "On-line". You went into a sports shop, tried on different brands & models, then selected what you wanted, imperfections & all. You took it home & proceeded to work on breaking it in. No special solutions or methods. Just a lot of elbow grease & a lot of catch. Now the vast majority want pretty much game ready. (I'm not speaking of the die-hards on this board, of course!)
Something I've always wondered about is why none of the glove makers source leather from New Zealand which is pretty much free range? I guess that it's an expense thing.