I definitely take some issue with the supremely underwhelming height here, but the blank walls are unfortunately a zoning anomaly. As long as there remains the possibility of building on the remaining neighboring lots, if they build to the lot line, it has to be blank. No developer wants to deal with windows they just put in being literally bricked over should another building rise next door. The same issue existed with the Westin, as it does with numerous buildings in New York that I've seen as well.
The Austin city planning department could (if they don't already have such an protocol) potentially provide the option of letting a developer sidestep that if there was a guarantee that the neighboring buildings would stay as they are. However, the only way to really do that is if those other buildings are zoned for no more height or density, or are historic structures or within a CVC, etc. Perhaps it's something they should look into examining...until then *best Oprah voice* YOU GET A MURAL, YOU GET A MURAL, EVERYONE GETS A MURAL!!!