In general, I think it is rather nonsensicle to believe that existing industries can ever block the entry of newer and better technologies to the market. If you just look at the products we are using over the last decades, it is clear that there is rapid development across the board and each bit of progress was to the detriment of other companies or even entire industries, who were profitable, rich and powerful before the new competitors arrived.
Specific to hair loss, I think that "the cure" will most likely be a expansion of the market rather than a decline. Let's say Stemson makes it and the price their product at €50.000 then that will be far more than an individual would spend even on hair transplants, minodixil, finasteride and other garbage.
I also wondered why a guy like Musk didn't commit a billion or so to solving this problem. My only explanation is that most billionairs are a little bit older and might still feel some kind of shame in solving a purely cosmetical issue like hair loss (Yes, I know it can affect mental health, but this is the perception most people have) since that is quite common in older generations. My guess is that they want to be seen as tackling real issues instead of engaging in vanity projects.