People had e-commerce apps long before there were SPAs. Amazon is not an SPA. The main reason to make an e-commerce app be an SPA is because you want your competitors to win.

To create a training set you might have to ask people 1000 to 20,000 questions like "Is this a dog or a cat?", "Did the patient survive the operation?" Usually you're asking the same question about different prompts, for instance, photographs or clinical case report. Answering a form is called "making a judgement".

If you're adding a new task (say "click on the person's nose") you need to add a new form. In an old-school web app you can add a new form when people are making judgements, there is nothing to it. In the case of an SPA you might need to make a new React component, compile the app, force people to reload it, etc. It really slows the process down.

I just read up on MobX and came across Mantine so I am leaning towards React again.