I find the shifting quality doesn't last in our sportbikes when using Rotella. So I use oil that maintains slick shifting throughout the oil change interval in our bikes. I'd use it if it performed better in our bikes. I'd certainly save money.
Why do people use it? the same reason you use a car tire on your bike. It's cheap, and apparently find the performance acceptable for their use.
Not all flavors of Rotella perform the same, and even the same flavor will usually perform differently in different bikes.
I can't speak to race bikes because I don't own one, but I use a few different Rotella products because they work well for me, even compared to other, more expensive oil options.
My VT750 Shadows prefer the performance of T4 15w40 over Castrol Actevo 4T 10w40 and Honda GN4.
Compared to the Actevo 4T, the T4 shifts smoother, and the engine is slightly quieter too.
Compared to GN4, the Rotella T4 holds shift quality longer and doesn't seem to sheer as much.
The T5 10w30 is the quietest and smoothest I've tried in my CB1100. The Honda GN4 was okay, but it sheered down to coffee water in just 4k miles, half the recommended Honda OCI.
The Rotella T6 15w40 wasn't a good match for the CB1100 either. Far too much engine noise and the shifting slipped sometimes.
But the T5 does a good job in the CB.
It's not because it's less expensive, it's because it works better.
