Many years ago, I had the chance to talk with Entwistle. He told me that he bought multiple Danelectro basses because the strings would break easily, and there was nowhere to buy replacement strings... so he had to buy replacement basses.
...and that jibes with Wikipedia's take on it, as well:
"My Generation" also featured one of the first bass solos in rock history. This was played by Entwistle on his Fender Jazz Bass, rather than the Danelectro bass he wanted to use; after buying three Danelectros with rare thin strings that kept breaking easily (and were not available separately), a frustrated Entwistle used his Fender strung with nylon tapewound strings and was forced to simplify the solo.