Unlike a lot of mobile games FFXIV wasn't designed with jump potions or similar boosts in mind. So it can be argued that buying them is playing the wrong way in this game.
At top tier crafting you really need to know what you're doing to succeed. Or go to a website that tells you what to do. That such sites even exist proves that people don't know what to do often enough to warrant an outside source that guides your entire rotation ability by ability.
Also while low lvl crafting doesn't require skill, it does require patience. Something which seems to be in short supply among a lot of gamers these days.
No it's not. Standing in line doing absolutely nothing isn't the same as crafting items to gain xp. In the first you're doing nothing, in the second you're doing something. In order for it to be the same you would have to somehow gain crafting xp by just standing around for hours doing nothing.
But that does nothing for the game economy issue. There is a massive economy for crafting and gathering for lvl 20+. The jump potions would ruin it because suddenly a gigantic chunk of what's for sale in the market would become meaningless. Furthermore this would punish players who cannot afford to buy jump potions on top of a sub, because they would be unable to make any decent money until they're high lvl. Crafter jump potions would be pay to win that would ruin the game's economy.
And again I emphasise that crafting is side solo content. It doesn't stop you from progressing in the main part of the game. At least for msq and combat class lvls you can make the argument of "I want to play with my friends in the content they're doing right now" because those two aspects of the game do require potentially significant progress to engage in a specific group activity. Such an argument can't be made for crafting because 99% of it is a solo side activity. You rarely get into a situation like "sorry you can't do this activity with us because your crafting is too low" but you often can for combat classes and msq progression.