Why would anyone ever want to dump/restore if you can just use pg_upgrade?

Question

pg_upgrade (formerly called pg_migrator) allows data stored in PostgreSQL data files to be upgraded to a later PostgreSQL major version without the data dump/reload typically required for major version upgrades, e.g., from 9.5.8 to 9.6.4 or from 10.7 to 11.2.

Source: https://www.postgresql.org/docs/12/pgupgrade.html

My related questions:

1. So if there's this nice, sleek pg_upgrade tool to do this in a much nicer and quicker way, why would anyone ever want to go through the whole dump/restore ordeal? I never knew about the existence of this until recently, and now I feel "something" for wasting so much time and effort when I could've just done a simple command.
2. I'm not sure why they call it "dump/reload" here. Isn't it "dump/restore"?

Answer 1

You can't use pg_upgrade on machines of different architecture. Or even just different available encoding/collations. You also can't use it to take multiple databases under different clusters, and put them under one. Or vice versa, break multiple databases under one cluster apart.