The long term hand baggage issues are stoked by basic economy/HBO fares, but the proximate issues must be the known unreliability of baggage systems. BA would have fewer problems with this at the moment if they would have working and reliable baggage delivery that passengers trust at all their airports.

I have to say that in my most recent set of flights involving plenty of hold baggage checking and retrieval, everything came out very rapidly every time, but did I trust it? Not at all. I had an extra-full (therefore extra-large) carry on bag compared to usual, with some spare clothes in it, and an elaborate set of bags stashed in my car parked at LHR to retrieve in case I ended up with no spare clothes half way through the trip. The Gods, after all, help those who help themselves.

I used to trust bag delivery until this year, when bags were not delivered for days after flights earlier this year. Re-gaining my trust will take some time.