iserith
Magic Wordsmith
I don't find knowledge checks especially useful, honestly. I think it takes a lot of effort on the part of the DM to purposefully add in uses for knowledge checks, and unfortunately, they've removed a lot of cool ones. Like knowledge of masonry used to actually be really useful if you wanted to destroy a building, or just avoid being destroyed by a building, and that's just sorta gone. What's left is pretty much three checks that are almost entirely to find monster weaknesses and abilities that I feel you don't really need to know immediately, and one check for world lore (which is sometimes pretty useful still during RP).
Any fictional action that involves recalling lore that is not Arcana, History, Nature, or Religion just falls under a general Intelligence ability check. So if a player says, "I try to recall what I know of the weaknesses of this particular type of masonry..." and the DM thinks the result of that fictional action is uncertain, then an Intelligence check could apply to resolve the outcome.
If you personally aren't finding Intelligence checks useful, then it makes sense that your players are dumping Intelligence. Knowing what a monster can do at the outset of a fight is very much a boon to the players, who can then potentially use what they discover to give themselves an edge. There are many other times an Intelligence check might come up, depending on the situation, when engaging with the exploration and social interaction pillars of the game. It's just up to your players to engage in a fictional action involving mental acuity, accuracy of recall, or the ability to reason and succeed at an Intelligence check the DM calls for (if the outcome of the fictional action is uncertain). Then it's on you as DM to reward success with a tangible benefit e.g. taking the time to deduce the workings of the trap makes it easier to disarm or analyzing the runes for patterns gives the PC a useful clue for solving the puzzle. In short order, I bet you see players investing a bit more in Intelligence.
Though this does make me wonder: In your game, do players ask to make ability checks (or make them without being asked) or do they just state fictional actions and wait for the DM to ask for ability checks?