Users just want pages to load fast. UI developers (presumably) just want to maximize user happiness. A SPA is just a way to front-load resources for a website

Users just want pages to load fast. UI developers (presumably) just want to maximize user happiness. A SPA is just a way to front-load resources for a website so users don't have to re-load redundant resources for each new page. Whether that is actually worthwhile for the user depends largely on how many redundant resources a site has and how many pages a user is likely to request in a single session. SPAs are a situationally useful tech just like blockchain, machine learning, JS component frameworks, etc.