>Think what it would be like if we applied that idea to the real world, so (e.g.) hammers, can openers, toilets, and bulldozers all had to operate using a common set of widgets.

Only apps don't do that. Paint apps use brushes and canvases, spreadsheet apps use cell grids, music apps use notation views and piano rolls, writing apps use document screens, games use whatever invented controls and worlds, etc.

What is common is that a lot of stuff we do involves mere text and symbol manipulation (buying tickets, reading news, checking sports scores, entering customer data, etc). For those we use the same widgets, yes.

But in the real world we do build all kinds of stuff, from cars to boats, and from skyscrapers to bulldozers, to pinballs with nuts, bolts, screws, wires, glass panels, etc., too. A hammer is as useful for hanging a frame as it is for building a house.