> Standardized connectors and outer dimensions for engines even between brands. Medium, large, small. You don't need 100 different types.

There aren't 100 different types of engines. At any given time each auto manufacturer only has a couple different engines in production. Different models can get different variations for performance or use targets, but auto manufacturers are very good at standardizing within their company.

Look at the list of Honda engines: https://en.wikipedia.org/wiki/List_of_Honda_engines

Notice how they're grouped by series? All of the engines in each series share a common platform with minor changes from year to year. In many cases you can swap parts between engines within the same series. An engine series lasts 10-15 years. Some times the parts even carry over to the next series.

Swapping between brands is a pipe dream, though. Forcing everyone to fit their engineering into a bounding box that has to be agreed upon by all auto manufacturers around the world would only lead to either unnecessarily large vehicles with wasted space (to leave room for future engineering needs) or unnecessarily complicated engineering to fit everything into the pre-defined allowable engine envelope. All to accommodate engine swaps between manufacturers which is never necessary for consumer cars.