But there are big downsides too. Mainly the market discourages ownership on the one hand and encourages piracy on the other hand. The result is that DRM protections are everywhere and some authors like Jonathan Lewin were burned up by e-book piracy and reverted to only physical copies. Also for some reason e-readers perform badly with technical writing (many references) and math formulas. It's not a technical barrier, it's just that the software is not optimized for these use cases.
Also showing off huge book shelves is impossible with an all-digital model. Some people care about that.