Economical they reckon.
Apparantly the RR was the better choice for the routes BA planned to use the new ER aircraft on, so they went and got Rolls (good choice if u ask me - i would have done it a long time ago.)
The GE engine was simply financial. they sold a maintainance centre or somehting to GE, and so GE said be our launch cutomer for the 90 and we will give u a nice discount.
The GE deal taking over BA's engine overhaul facility, was seen as shabby. It almost knocked R/R out of the big fan market, (All Nippon were leaning towards R/R for 777's, BA's shock buy of the GE90 apparently influenced them away from the Trent, the city in the early 1990's were predicting that R/R would end up a junior partner to P&W or GE, it took a couple of years for R/R to get new customers and eventual success in that market).
GE's take over of the engine facility has ended up costing BA, staff morale there dipped, experienced people left, and BA ended up having to do some of the work at LHR.
But the real clincher for R/R for the later 777's was that BA suspected that GE could not provide a higher thrust GE90 quickly, on some routes BA's early 777's were having passenger restrictions of up to 60.
Pilots like the GE90, engineers less so, at least in the early part of the 777's service.
When the 737NG and A320 series were competing for the BA order in 1998, many of us feared Boeing could win by offering to buy BA Engineering, similar to how GE won in 1991, Boeing had talked of setting up an MRO facility in Europe with a major airline at that time.
So it wasn't just a desire to see BA at last supporting UK industry by going Airbus, no offense to Boeing fans/employees here, but from across the pond we saw Boeing shedding 1000's of their own people (again), feared for our own security, not to mention losing the benefits of working for a big airline.
But aircraft choices apart, I think BA have learned from the GE deal.
There are bits of truth contained in almost every responce that has been given so far.
The GE engine was chosen for a couple of reasons, first being that on paper the GE engine is clearly the best engine- initial performance problems aside.
Secondly, Ge agreed to purchase an unprofitable engine shop that had been owned by BA, therefore the financials of the deal became much better.
BA soon became extremely unhappy with GE over the GE90, however. BA publicly stated in news accounts that they felt GE had used them as a guinea pig to test a product that needed more refinement. However, this dissatisfaction cannot be directly attributed to their order switch around 1995. What seems more likely is the affects of cancelling an order for 747-400s. The elimination of the RR powered 747's for a 777 order made them bound to Rolls-Royce in some fashion. ie. pay cancellation penalties, or order RR engines. The second reason is the most likely cause of the RR engine choice.
Yes, BA wasn't happy w/ GE, however, there was little indication before the 744 cancellation that they were considering a switch.
It is true that the RR performed better on SOME of the routes BA has used 777s on. And there was concern over GE's commitment to what was at the time a losing program.