Here is my take on why you are seeing more "upsets," which I don't think is just a Northeast Ohio thing:
1. Basketball is definitely more popular than when I was in high school (late 90s) and only seems to be growing in popularity amongst kids now (FWIW, hasn't translated to this site because lets face it, most of the people that still post on boards like this are 40 and older). But the sport is very popular with teens (not just Ohio but in just about every state ... as well as internationally).
2. On top of more kids playing, it has become so specialized. Fall sport athletes going over to basketball used to be the norm. Now, they are an outlier at most of the schools that you'll find at the top of these rankings. I'm guessing that the top basketball schools may average like 2-3 players who played a fall sport.
3. Being specialized has helped with continuity. "Tryouts" are mostly a dog-and-pony show. Coaches know earlier than ever who has improved and who will be on a team. And even if it's via open gyms, "practice" essentially now starts when the school-year begins. There is less of an adjustment period to try to integrate fall sport athletes, who for the most part not only take time to integrate with the team, but need a few weeks to get their basketball legs.
4. So many of these teams are also familiar with each other because they either have played, or at least watched each other play, at all the summer events that are out there (high school teams are playing basically full-season schedule's worth of games just in June by packing in as many running clock 40 minute games as they can). That is really where the tryouts are now. Coaches know who will be in their rotation and players that are on the outside have a couple months to figure out whether to stay or find a situation at another school where they would have a better shot at playing time (I don't see anything wrong with that; if a kid is willing to dedicate that much time into a sport and there are avenues out there to play, why not take advantage of that?)
5. AAU is also now so prevalent. There are so many local programs where even the kids who are joining one of the dozens of local teams are playing 5-6 tournaments in April/May (then maybe one out of state "national" tournament in July). The ones who get on one of the sponsored travel teams are playing every weekend in April and May and then playing every weekend again in July. For those players, they are investing 11 months of the year into basketball (August ... if they aren't playing a fall sport ... being the only month off). If they are in a situation where they may be roadblocked at their current school, I'm not sure how you could blame a family for looking for a different spot, especially since those are the kids who may be on the verge of a scholarship/college opportunity, but a coach/school wants to see a little more from them during the HS season.
You add it all up and it's not a surprise why all that has led to more parity amongst teams, especially those in bigger metro areas where there are more opportunities to transfer to a better situation. Going up and down the list of teams that are ranked in some of these various polls, I can say I've either seen every single one of them, or at least know of a player or two on any of them. Going up and down that list, hardly any are consisted 100 percent with kids who have not played at another high school.
That may be turning some older folks off who remember "the good ole days" when everybody played at one high school, but it's just not reality anymore and it's not going to go back to that. I say look on the bright side and embrace the parity it has added ... you know like Lutheran West being able to beat Ignatius by 20 then turn around and lose to Holy Name less than a week later. ... Or Walsh beating SVSM and then Stow beating Walsh. I've gotten to know people over the past 5-6 years on all of those teams mentioned (all are very good teams, btw) so, for me, all these "upsets" weren't monumental and it just adds to the intrigue of the HS season, and should carry over to the tournament.