Simplicity. Some people don’t want to fuss with tubes, checking, or replacement.
There are times I take the tubes out of rotation and play a nice Class-A solid state amp for a while. In the future, when I consolidate the system back down to a simple footprint, it may be leaning back towards a nice SS integrated amplifier unit. For now, hearing the tubes do what they do is worth the extra bit of time and fuss to me.