Three reasons why:
1. Srpska's today territory was with about 48% Bosniaks pre war, and Serbs were found to have committed genocide on Bosniaks.
2. If the Bosniaks are left alone, they'll become an Islamic emirate. No one wants that.
3. Croatia doesn't want Serbia on that long and hard to defend border. Bosnia will serve as a buffer. In fact Croatia threatened to wipe Srpska out if they declared independence (specifically forbidden by Dayton.)
Map for reference
4. As a bonus, no one is itching to have a strong Serbia, certainly not Germany, US, UK, Italy or France.
Seeing what a mess that secular increasingly muslim Europe have made of things — all Christians including “Catholic” Croatians should all be rooting for a stronger Orthodox Srpska and Serbia.
Another history revisionist troll on a Balkan thread.