Hybrids are attractive when a short battery range is enough for daily use but you still do semi-frequent long-range driving. Rather than hauling around a heavy and expensive XL battery pack on your daily commute you haul around a tiny combustion engine. It's a great solution for people with range anxiety.

Buses have a completely different use case. They drive a well-known distance, and every day is practically identical. It is fairly easy to scale its battery pack to closely match the actual range needed. Running a true long-distance route like a Greyhound or Flixbus, which physically can't be battery-based yet? Just stick to diesel for now.