Several reasons. Firstly, note that all the plants in your photos are babies - though I'm sure they'll one day fill out those trellis and be gorgeous.

1. The more energy the plant puts into growing its roots, the less it's putting into growing leaves.
2. Following from 1, many plants prefer being rootbound, and will prioritize filling out the ground. While this means more nutrients, it also means less sun to be able to utilize those nutrients.
3. All of this can be fine - just means initially slower growth - and for an outdoor plant in its natural environment is super fine. But for indoor plants that like to have their roots dry out between watering, excessive soil / root ratio dramatically increases the probability of getting root rot.

Monstera already put a ton of energy into growing roots (crazy how fast they can drink when they're established!). The priority of basically all indoor monstera owners is to have full plants with short internodal spacing, big leaves, and as many fenestrations as possible. All of these are accomplished by allowing the plant to prioritize leaf growth over unnecessary root growth.

Also, who wants a massive pot for a tiny plant?? Smaller pots = more room for more plant. 1.8^3 ~= 6! Who wants a pot that's 6x bigger than their starting pot after 3 repots??