They started doing it in reality TV, where writers don't have union protections and are easy marks for getting this kind of material in there. You're less likely to find it on network prime-time series, but the creep is moving in that direction. It has become intrusive and overwhelming to us as a union of writers.
For actors and writers who are being forced to shoehorn products into their work -- whether they fit or not -- there are critical issues of creative rights, consultation and fair compensation. For the public, there is the serious matter of disclosure. Consumers, parents and all viewers have the right to be told when we are being sold.