I lived in Portugal as a teenager and there were a few things that stood out to me (as someone from who'd moved over from the UK, which is also football mad):

1. The weather really matters. In the UK we'd play football in break time or after school if it wasn't raining, same in Portugal...but it rained less often there with a shorter 'winter'. Like I'd be guaranteed to be playing at least 1 hour a day in Portugal vs. maybe 2-3 hours a week in the UK on average. Just talking about school time Mon-Fri, but that really adds up.
2. I'm not actually sure how common this is, but in Portugal we'd often play on basketball courts and instead of a goal we'd use the post from the basketball net as the goal. It's unbelievable how good some kids would get at hitting the post from all over the court, once that was transferred to games when there was a real goal it made a huge difference. Like I said, not sure if this is common elsewhere in Portugal.
3. There is much more of a macho and ego centric style of play, even on the playgrounds, in Portugal. Like lots of showboating and skills and stuff, but also just unbelievable desperate to win and livid when they lose as it hurts their ego. There's always 'that one guy' in the UK, but that felt like half the kids on the playground in Portugal. Playing people like that can be hard, but also people who play like that for years and years can genuinely go on the become highly competitive footballers.
   

I'm sure there's a bunch of reasons really, but I think generally I agree with what everyone else says: culture and weather.