The tradeoff is this:
1) PMs get broader visibility across the org, which tends to result in faster promotions into management for "good" PMs.
2) PMs atrophy technical skills and become more dependent on the larger organization (they acquire more firm-specific skills in econ talk) than do equivalent developers.
So, sometimes if you like your company and want to advance quicker, you will be willing to trade away some industry or general skills for firm-specific skills to get faster promotions or more power.