Despite SpaceX's high-tech reputation, SpaceX aren't where they are today because they made massive technological leaps or pushed the envelope of science--after all, just doing science doesn't earn money. SpaceX doesn't have some "secret sauce" of IP or some secret, hyper-advanced engine technology that makes their engines an order of magnitude better than the competition.
In fact, with only very few exceptions, basically all of SpaceX's successes have come from streamlining the production of known technology to a ridiculous degree and getting the assembly lines and processes down to a science, which is, in Elon's own words, where most of the effort is (in an interview, he states that compared to production, design and development is simple). SpaceX primarily optimizes to price and dollar effectiveness, not individual rocket efficiency.
Throughout SpaceX history, they've consistently dropped advanced and cutting edge technologies, favoring simpler and straight-forward solutions under their "the best part is no part" design philosophy. One good example of this is how the ITS/BFR/Starship system used to be conceptualized as a massive carbon fiber construction, before they decided that the gains achievable with this material wouldn't outweigh the development, research, and other costs associated with it--they figured it would be simpler to just eat the minor hit to mass and make the whole thing out of steel, and so they did.
I suspect a similar thing has happened with the transpiration cooling. Elon likes to kick around wacky ideas, and that's his role as the CEO: he provides vision and fulfills the 'dreamer' role. Doing so causes lots of people to talk and think about the issue, and then a more informed decision can be made later. (Ablative) heat shield tiles are the simple solution in this case. No moving parts, no valves, no complex fluid dynamics, decades of experience and flight heritage, etc. When there's a tried and tested method of doing something, there has to be a very good reason to go and reinvent the wheel if your primary goal is profit.
