So why can’t we alter the materials used in manufacturing that adds buffs/debuffs to the thing created.
Say you use cheaper materials to substitute more expensive material puts a debuff on said gear with potential of it causing damage to its self similar to overheating.
While using more sturdy materials adding addition buffs to the gear but being far more expensive this would add a level of personalization when manufacturing stuff for those builders in eve.
Because of two things: game optimization and game balance.
There are two types of items in the game: packaged and unpackaged. All packaged items of a specific type have their unique ID in the database, which allows them to be listed and sold on the market. When an item is unpackaged (for example: a ship is boarded, module is added to a ship or removed from a ship), you have another ID which reflects that specific physical item. This ID is removed when the item is repackaged.
Those are the basics, so lets see why it’s not a thing.
Yes, you can modify attributes of some modules with mutaplasmids, but that’s a very limited set of modules. Because they are modified, they can not be sold on the regular market, and because of that their trading potential is extremely limited. One redeeming factor is that you can apply a mutaplasmid to a faction or officer module and, if you’re lucky, you’ll get insane attributes that would make the module valuable and sellable - but only on the contracts, because that specific item with that specific physical ID is unique and cannot be sold as a generic repackaged item. This, however, comes at the cost of using pure gambling mechanics which has its own significant downsides.
Scaling this up to all ships and modules and removing barriers (like gambling mechanics), does not make any sense at all. Take a Punisher (ship) as an example. It costs about 400.000 ISK. and needs 4 types of materials to produce. This means it’s mass produced - most likely in much bigger quantities than all mutaplasmid items combined.. Whatever you do to limit the number of possible combinations of materials, you will end up with a lot of different item IDs that are NOT a Punisher. Listing hundreds of versions (or even 5 versions, for that matter) of a Punisher would be at best confusing and increasing clutter and at worst technically impossible to implement.
The second point is game balance. We already have too many different types of materials, reactions, components, ores,… And we constantly have bottlenecks and game breaking balance problems when some material gets even slightly out of balance. Sometimes it’s CCP’s fault, but sometimes in-game player actions are the cause to disbalance. Having to detect what exactly went wrong and how to fix the balance when you have a variable list of material requirements is just plain impossible.