My 2 pecs:
When you buy anything for a large amount of peds, most players want to be able to get their money back at some point - or at least feel they haven't lost the peds forever.
If you buy an a104 amp today, you know (or are at least 95% sure) that you will make a profit if you sell it in maybe a year or two. Same if you buy a big gun or uber fap. This is because demand outstrips supply.
But if you buy skills, e.g. Handgun, you know that you will lose money, because prices have been on a downward spiral for the last 18 months and nothing is changing to correct this. If you ever sell the skills you can be virtually certain you will lose money. This is because supply outstrips demand.
Basically unless
MA somehow changes the skill system, the value of skills can never ever increase again in the long term.
If you want to sell some of your gazillion skills in the future, you may not be able to as they will be worth nothing. That is my point...