I don't think the issue has been as prominent because black footballers haven't been as common over the years as white footballers, it's really in the last 20 years or so you've seen more black players at the highest levels, in the best clubs.
Whereas NBA especially has had decades of dominance from the black players.
Onto your point about white players finding it difficult to break though - basketball as a professional sport is played mostly by white people globally, I don't have numbers or statistics to back that up, but at collegiate level in the USA, plus throughout Europe its a mostly white sport.
The focus is of course on the NBA because that's where the best talent is, most exciting plays are etc, similarly with the NFL.
The conversation on why that is dominated by black people, and assuming it's because black people are naturally stronger is lazy and only further highlights just how racist stereotypes are embedded even subconsciously. Don't get me wrong, I'm not saying you (or anyone else) is a racist for thinking this, no. Just that it's not as simple, and certainly isn't the only reason why these situations occur.
I'll explain - you can't say a statement like that without looking at the wider context that surrounds the conversation, historically in America black people have a history of being denied opportunities to succeed, and black communities & schools have been underfunded - we don't need to go into details everyone knows the story.
Sports has always been seen as an escapism for a lot of kids to avoid drugs, gangs, crime etc and sports stars are seen as celebrities, they're rich, they get the girls they live a certain lifestyle that is enviable.
Now when you couple those two influences together you get black kids who find it harder to get into traditional avenues to be successful - business owners, lawyers, doctors etc so instead they rely on sports because if you can dunk at the age of 14, a scout isn't going to pass you up just because you're black.
That means it levels the playing field a little more you are assessed because of your ability - watch any sports documentary that focuses around poor black kids and you'll find a common theme - they work hard because they didn't opportunities, they've had to compete all their life so sports feels more natural, and they work hard to improve their skillset.
On the other hand, if you're a white kid who's very good at sports, you will have been given a scholarship to study and you'll at least be more open to the idea of taking a more traditional route to success because you haven't had to face the same lack of opportunities that the black kid will have done - and you won't have the fear of being rejected for job interviews because of things about you that you can't control or change.
(Yes I realise i'm generalising, and yes I understand that these two situations wont apply for everyone - however it's important to highlight that these are very common situations)
If you ever watch any sports documentary that's centered around poor black kids who have gone onto reach the highest level at their sport, or have aspirations to do so - you will see this theme being very consistent. Last Chance U on Netflix is a fantastic example, but there's so many more.
I could go into this further, but the main point is that to suggest that black players dominante the NBA & NFL because they're physically stronger than white players is dangerous & lazy, and takes away from the hard work and sacrifice that they will have put in to get to where they are. It suggests that they are somehow born to be better equipped than their white colleagues, and i'm not discounting someone like LeBron James being a physical specimen - yes he absolutely is, some people are born unique. But someone like Kevin Durant is tall, gangly, awkward but is arguably the best player in the league right now because he works hard - similarly the Point Guards are usually the best players in NBA and they are (usually) the least physical.
Black kids are attracted to the NBA & NFL because of the money involved, and in a lot of cases sports has been the only thing that has given then them a chance to better their life.