Re-engining is a lot more expensive and complicated than you think. It causes major restructural and engineering complications, weight and balance problems and design considerations. It has to be tested in airflow chambers, extensively engineered, flight tested etc. It is VERY expensive. Worth doing for a big program like the KC135, but otherwise, the old airframes don't have the life left in them to make it really cost effective. It really is simpler to start again with the latest passenger-attractive equipment. Those old airframes have far higher maintenance and reliability problems. You're really only putting off having to upgrade at some stage.
I could have been driving round in cheap old bangers for years, maybe even re-engining them. But it is better to get a shiny newer BMW and experience quality, comfort, reliability and more street cred. Better to let my old bangers get scrapped, or shipped to places in the world where people will keep them going, but they'll keep breaking down! Just the same with aeroplanes!
European carriers definitely favor Airbus products.
Not sure I agree! European airfields often look like Boeing Field? Tell that to Ryanair with 170(?) 737-800s. Looks to me like Europe is pretty evenly split, even possibly in Boeing's favour. It all comes down to doing the deal with the man on the day!