Paul made a colossal mistake in appointing Tommy Bilotti underboss!
I dont doubt Billoti was a tough SOB and in a road rage incident or a fight I would want Billoti at my side but to make him underboss was pretty much an insult!
Castellano hated Gotti and vice versa, Gotti only lasted in the family because Paul knew that whacking him would cause loads of Friction with Neil.
With Neil gone, Big Paul figured he could finally humiliate Gotti and bust him to soldier and take his crew off him.

Gotti was backed against a wall, he had no choice other than to order the Sparks Steak house hit.

It has been said that Big Paul lasted as boss because of two men.
Roy Demeo and Neil Dellacroce.
Demeos crew was feared by nearly everyone and was Pauls main piece of artillery in a fight.
The other was Neil Dellacroce, Neil was respected throughout Cosa nostra and had loads of power.
With both of those men out of the way, Gotti was free to act!