they may not have had to ferry the plane from the alternate airport.

the alternate airport may be the standard used for that airline, and is set up to accept and handle extra incoming.

the alternate may have had proper crew facilities.

for a couple asides. northern italy has a lot of fog problems in winter. psa is the alternate airport.

once when lhr was fogged in, we were diverted to cdg. cdg had no facilities to handle the issue. we sat on the plane for 6 or 7 hrs until the fog back at hr lifted.( that was a few years back, we were on twa)