Why so many tubes?


Many of the most expensive tube amps/preamp have multiple tubes...6, 8, 10. If direct path is preferred in the speaker by most, why the acceptance of a glass army in one's amp/preamp? 
jpwarren58
There are always different ways to approach a task.

If you want simplicity in the signal path, start with high efficiency speakers, dht single end triode integrate amp and a source.

more watts require more tubes. 

I don't use high power (Lamm ML2 SETs in the main system) but everything from phono stage and power supply to line stage to amps is tube circuitry so I do use a lot of tubes. That in itself is not a problem. (I like to think of them as "field replaceable" parts that solve some, not all, problems). The difficulty is finding good sounding tubes that satisfy--and in that, I don't mean to be a snob-- to the contrary, a modern circuit that can work at optimal level with current production tubes would be preferable to having to hunt for increasingly scarce, and expensive, NOS that is fresh. 
With tube gear, I've had pretty good luck since the early '70s with medium powered amps (70 watts or less) and minimal issues with tube preamps. My current amp set up is the above Lamms-- pretty simple and lower powered at 18 watts per amp-- or in current operation, some restored Quad IIs running real GEC KT 66s. 
I haven't counted how many tubes are in circuit in either system, but it's probably a lot. I replace/refresh when necessary. It's part of the routine operating cost of tube gear, with the above caveat about sonics and NOS/scarcity and cost. 
For non output tubes sometimes a gain tube is followed by a cathode follower which is sort of an electronic transformer to lower the output impedance of a gain tube so it drives the next gain tube better. Goof examples are 1970s and 1980s Audio research amps and preamps.. This effectively can double the small tube count.

Another possiblity(which can be also combined with cathode followers) is push/pull voltage gain stages. This doubles the number of small tubes also. Again look at the Audio Research products from the 70s and 80s. Push/pull needn't be used for voltage gain even with push/pull output amps. And many preamps are single ended too even from manufacturers who made push/pull tube output amps.
if the op is seriously asking the question, the answer is quite different from preamps and power amps

each has reasons, different reasons, to use few vs multiple tubes 
I suspect a troll or lazy OP. All it takes is to Google “audio vacuum tubes: advantages, disadvantages, and uses in audio”. Also, learning how an audio signal is amplified is also readily available online.