There are games where a player has different abilities and powerups to give them an advantage in gameplay. A lot of 2D Super Mario games have powerups you consume immediately upon contact and an extra powerup you can summon at any time. There are also games like Resident Evil that give you limited space for your items. Souls games allow you to carry absolutely all of your equipment in a menu and switch at any time. I'm just curious, what goes into the thought of how easy it is to allow a player to access their tools?

There are some downsides to having the player be able to carry everything and having that stuff always available to them. In Final Fantasy 15, a common complaint was that the dungeons were trivialized because you can carry an absurd amount of potions, max hp restores, stat boosters, and revive items. I saw gameplay of an arcade horror game, Dark Deception, that gives you all of the various powers you can obtain all at once at any point. This could make the player overpowered, but it also seemed to make the gameplay more frustrating, having to cycle through each powerup to get the one you want. 

Dragon's Dogma limits the player with through item weight. In my opinion, I find this method fun and it's my favorite one so far, but I can see how a lot of different players get annoyed at their speeds getting hindered by carrying too much stuff. 

But then, there's always the simplest, and most common, way of doing this, and that's a direct item amount limit. 

This boils down to what game mechanic you want to implement. Games, gaming, playing a game is about rules and optimisation.

 Oh sure, there are other things that are also called "games", but are not games according to the gaming definition but according to other criteria, like having a non work fun experience. Kinetic visual novels are not games just like snakes and ladders is not a game. You have zero control over the outcome, you cannot "game".

what goes into the thought of how easy it is to allow a player to access their tools

Not much in most cases, I would guess. Monkey see, monkey do. I believe that games can be made better if there is actual thought put into this. What is the game about? Is it about the boss fights, the story, multiplayer aspects, manual dexterity, puzzle solving, etc?

If your game is about resource management, obviously this part of the game should have a lot of focus and be made well.

For other games, resoucre management is often just a thing of quality of life and the developer either not putting development time nor thought there. If your fights are made in a way, that you can power through them, if you just had enough health potions, those fights are badly designed.

Unless of course you plan your resource management to be part of the fight. Rogue like deck builder games come to mind.

But also, if you want to have outside combat resource management. You need to earn the gold for those potions in the first place. If that is hard to do, that is your limitation. If it is too easy, you can limit the inventory. You might want to bring some plausibility and immersion into this, like having weight or carry limits. But that can also just lead to players loading a save game and taking the right equipment with them.

So, as I said, it depends on what parts of the game you want to be gameable and be part of the game mechanics.