why cell phones don’t authenticate the towers they connect to.

I believe it's because they assume it's not necessary because it was until now

• prohibitively expensive, but now a "tower" is less than 2k EUR e.g. https://www.crowdsupply.com/ukama/ukama
• prohibitively complex, see above, namely you don't need to be a TelCo engineer to get it going
• probably illegal, namely you needed (and I bet still need in most places) wireless band allocation before you could deploy anything

... so I imagine there was no authentication because there was no practical threat beside few "fun" examples in CCC or DEF Con.