1. People generally fear originality until it receives sufficient social validation, but by then your business is established.
2. People generally cannot copy anything original after a certain point of complexity without motivation well into unnatural territory. For example nobody is going to quit their jobs to replicate your unproven idea because the effort is too high for something completely unused.
A rare exception to those two points is Minecraft. They replicated the idea of a sci-fi voxel game from scratch, changed the scenery, and kept in beta for years.
Technical work let's you enter the field, but the survival depends on the squatting in the supply chain routes or locking away your customers in your dungeons.
People and other businesses buy services and products for a myriad of reasons; sure, cost and convenience will weigh significantly more than others, but the decision-making is never down to the idea or cost alone. In fact, after cost and convenience, trust plays a very important role; and this is translated in a number of ways, from the ability of an entity to deliver on its promises, to safety and security (where applicable), potential for growth alongside the buyer's needs, penchant and budget allocation for innovation, how it treats its workers or behaves in other respects (brand value stuff: environment, stakeholder engagement etc.), easiness of collaboration and communication, the quality of support, whether they're willing to risk losing some money in the short run for the sake of long run success (i.e. being ready to reimburse some costs for a client beyond what's legally required when it fucked up), whether the provider speaks the same language, whether it's based in a jurisdiction where the buyer can trust that the seller is not green- or white-washing on its commitments, and so, so many other factors.
It's not uniqueness of the service or product that drives success or keeps a business afloat, but a combination of factors.
Now problem is, because people from outside usually don't know it, and believe they are relevant, they used to create the vast majority of "investment" demand for coding... and now because they ask themselves the same question as you did, they just stopped trying, and their demand is gone.
Because the reality is that 99% of a startup’s success is in the boring grind of doing marketing, sales, development, customer support, accounting, on and on.
Actually making the simple app is the easiest part of the process, and always has been, even before AI.