I have been happily buying units of IVV commission free via TD Ameritrade. They just revised their list of free ETFs and sadly IVV is not one of them. Most of the other institutions don't offer it free either (Fidelity does but I have some other issues with that).
So I'd like to know - what factors affect the likelihood that an ETF trade would be offered commission free (in the past, present or future)? For example, did Black Rock have some kind of temporary marketing strategy to build their fund capital? Was Ameritrade cutting costs and found that their strategy to make this ETF free was not profitable overall?