Conventional theory suggests this would occur under conditions of increasing market power. Most of the symptoms of this (of which decreasing investment is one) can already be witnessed. [2]
It seems therefore that the increase in share buybacks is simply one of the symptoms of the overarching market concentration narrative. Monopolists have little need to invest/innovate due to lack of competition and are therefore free to commit resources to price manipulation or further increasing their market power.
In this context any anti-buyback campaign would prove ineffective unless carried out alongside policies designed to limit market concentration and increase competition.
[1] https://promarket.org/responsible-declining-labor-share-outp...
[2] http://noahpinionblog.blogspot.co.uk/2017/08/the-market-powe...