This is not so much a concern per se, as it is a curiosity with my Monstera Deliciosa plant: It is not a small plant by any means and I've had it for nearly two years now and it seems to be thriving and growing just fine (in fact I have to prune it back to keep the size in check). The weird thing is that it has never developed any aerial roots, and I'm just wondering why that might be?

When I first got it, it was in this big 14-inch pot with no support so it had spread quite a bit. I got a moss pole and have "trussed it up" as tight as I could without damaging it to encourage more vertical formation. But neither one of these conditions ever made it develop the aerial roots that I've seen on other Monsteras... even much younger/smaller ones.

Are aerial roots environmentally triggered?

Aeriel roots are promoted by damp surrounding air or contact with damp surfaces. In nature, Monstera is a low-growing (not upright) plant that sends out long vines along the damp rainforest floor and puts out roots that go into the damp soil. The vines will also develop roots when in contact with damp tree bark and that enables them to climb the trees, sometimes in search of more light.

When moved into pots, that aerial roots no longer serve a purpose. Nurseries like to attach the vines to moss-filled or bark-covered stakes in the pot to get them to grow taller and increase their marketing opportunities. In their greenhouses, they can do this because the air is very humid and they can keep the stakes wet at all times. That is much harder to do in our homes, hence we end up with elaborate methods of trying to support the vines.

Personally, my preference is to keep the vines pruned back rather than trying to make them grow upward. But that is personal preference.

Thank you very much for the informative response @WillC

I think I agree with you with regards to letting the plant have its original form, it looked a lot more "lush" and natural before I tied it to the moss pole -- it just took up too much vertical real estate in the apartment. Hopefully, after we move to our new place this summer I'll be able to find it a more spacious corner and take the pole and ties out.

UPDATE: I ended up having to re-tie the plant to the moss pole because the ties were too loose and they were coming off. This time I tied them closer to the pole so everything's slightly more vertical than before. Interestingly enough, within 7 days or so I see aerial roots coming in! (second picture)

So my guess is that this is similar to the holes in the leaves where "the higher" the plant thinks it is the more you get? I've also been misting the moss pole whenever I remember, but not with enough frequency to keep it moist at all times.

The aerial roots won't attach to the moss pole unless the moss is kept constantly damp and the roots are held in place against the damp moss. This is very hard to accomplish outside a humid greenhouse environment.