If there were a suggested change and the reason was realism, I think given the time and resources necessary they would change it.
The only reason NOT to change it (besides lack of resources), even from BB perspective, would be that the change would cause something else to not be ask they like...like if it imbalanced play etc. etc.
I don't think they are trying to make the game unrealistic. So I think realism is a valid argument for any change.
I would hope they think about it differently than you do, in this specific instance.
The primary criteria should be: "Does this make BuzzerBeater a better game?" Realism is a nice thing but many things that would make BB much more realistic would absolutely destroy the game experience - whether it be having to prove yourself as a scout for X number of seasons to even get a job as a GM (and therefore a team to manage), or whether it be that any good players that you develop are going to be picked up by higher level or more prestigious teams, that type of realism would be game-killing for an online game such as this.
Of course, addressing the foibles of substitution patterns would likely make the game better, at which point we're probably falling under the "we can't do anything currently about the match engine" problem. While there's certainly a good reason to prevent teams from setting specific minute totals up for their players, more control over the broad substitution patterns in the lineup decisions would be a welcome relief.
I just think any discussion about changes proposed that is relying on "realism" as the driving force is making a poor argument. The selling point should be how it improves the game and maintains the concept that you can't have it all - you may have to sacrifice training for results or vice versa.