The earliest recorded and transmitted singers did tend to be "lower voices" but it had little to do with the "delicate tubes" being "blown out" - in the sense of their being "broken" - by higher pitched voices and instruments. Because of the mechanical bits and pieces in the process, from recording machines thru microphones and ampiifiers, higher pitched sounds were very difficult to pass through the process, and as a result it was difficult for the transmitter to broadcast higher frequencies with the same amplitude fidelity of sounds nearer the mid-range, and virtually impossible for receivers of the earliest times to play them back, so sopranos simply didn't sound as good - especially at the receiving end. The "blow-out" refered to by broadcast engineers was the loss of good sound quality for signals far from the limited frequency range that the equipment could handle.
By the time of Sinatra and Crosby fidelity of broadcasting had improved to the point where higher voices could be included, but it perhaps remained true that the baritone voices of the male "crooners" and alto voices for females still tended to have less apparent static and noise and were thus more "pleasant" for radio listening.
While it probably was technically feasible to broadcast a different audio frequency range that might have been more favorable to other voice ranges, the main use of early radio was for spoken voice frequencies, so those are the ones for which equipment was optimized - to the extent that optimizing could be done.
Others with better knowledge of "traditions" may correct me, but I believe the term "crooning" dates to far before any kind of broadcasting was known or even thought of, with the connotation being that the singer is relating a love/affection for the object to whom it's sung. The "crooners" of the thirties/forties were so-called because they mainly sang "love ballads," which could have been done by singers in other ranges, but sounded better when done by singers with voice ranges closer to spoken voice frequencies(?).
The technical limitations that made sopranos less listenable than alto and baritone voices also tended to exclude deep bassos in the early days of radio, simply because no matter how well the signal was broadcast nothing much came out of the speakers at the recieving end. Clear enunciation was also needed for pleasant listening, so the singers of the times tended to choose songs with "verses" that could be understood(?).
The central point of it all is that in that earlier era "what works best" was more pleasant for the audience, so that's what got broadcast - and was most popular.