I'm a bit late to the party but I will give you my tuppence ("dimes") worth. I also haven’t read all the posts in the thread.
I'm UK based. I'm a little cautious of giving you the European viewpoint because I'm British, and the British approach is not always the European approach and vice versa.
The majority of cylinders in the UK are steel. Historically, where you have seen aluminium cylinders is where you are hiring cylinders, so more often European and Red Sea Liveaboards and dive shops where cylinders are being hired and abused (having the paint knocked off them). Generally Aluminium needs less maintenance
We had a big scare here a few years back with cracking in the aluminium, so a lot (in the UK at least) got scrapped (the test period got changed making it expensive).
The other issue is that Aluminium cylinders tend to change there buoyancy characteristics quite a lot, this has also historically made them unpopular (at least in the UK). They are also heavier than equivalent steels.
When I started carrying stages, the vast majority where steel, mainly because of availability, although aluminium is better suited as a stage cylinder.
The number of aluminium cylinders in the UK has significantly increased as the popularity of rebreathers has grown. The main reason for this is, with full aluminium stages, they are almost neutral in the water. So handling them, removing them, handing them off etc, is much more comfortable if you are on a rebreather than steels.
The popularity has increased so much that we regularly buy Ali80’s here. The only slight negative is that the fill pressures are low, around 205 bar instead of 232 bar, so you need to be careful when they are filled, that they are not overfilled.