Likely TUI (and its various airlines) will have it's own SOPs for ACE and bad wx
7 diversions - 4 were TUI - the 3 others thought the same - so ACE was a no go
(probably a TUI day lol)
Thursdays and Mondays were historically UK-ACE package charter days (likewise TUES/FRI is a TFS day and MON/THURS was a LPA day
FUE was WEDS and SATS)
not quite so rigid nowadays because of the all low-co's