The problem is that game design is difficult. One of the most prominent quotes in game design is that:

Given the opportunity, players will optimize the fun out of a game.

Source: https://www.designer-notes.com/game-developer-column-17-water-finds-a-crack/

Which means, if you make an item farmable, some players will subject themselves to hours upon hours of unfun gameplay, because it's technically more optimal to farm it. And if you make it more tedious, they will just spend even more time on it.

A big part of good game design is just avoiding bad player experiences like:

• Players optimizing the fun out.
• Skilled players waltzing through without any challenge.
• Less skilled players getting stuck, because they cannot handle the difficulty.

Giving less skilled players consumables can allow those players to progress when they get stuck.
Not giving an infinite amount of those consumables encourages skilled players to take on somewhat more of a challenge.
And genuinely just limiting resources rather than allowing farming prevents players from optimizing the fun out.

Ultimately, it's significantly less of a problem when skilled players don't use their limited consumables, than any of these other scenarios.

Having said all that, a genre where having limited resources actually works well, is roguelikes. Knowing that all your consumables and whole character might be gone, if you don't use some of your consumables in a dangerous situation, works wonders.
Of course, the downside here is that you likely exclude less skilled players.