Well if COVID and flying was as dangerous as many contributors to this thread are making out, I’d expect them to cancel to save their lives....
But no, I’m not buying it. BA Holidays and BA allow people to amend their travel dates, Tier 4 was announced 3 days in advance which is enough time for the majority of accommodation bookings to be amended/cancelled without a fee these days, and with the FCDO still advising against travel to Mexico, one would imagine those on this flight would’ve specifically chosen insurance that does cover them - or are so nonchalant about the whole thing they knew they’d be going regardless.
304 passengers on yesterday’s LGW-CUN so no anomaly either.