1. We are talking explicitly about your false statement "(straight) 22% increase in sales if game out on PC". Alternative scenario when game launch on PC only is a massive loss as there is no way 22% will grow to 100%
2. PC gaming player base are mostly f2p and very cheap stuff. It's not a core console projects "70$" target audience. Sales split 22%/78% already telling a story, this "huge player base" in equal opportunity buys 3.5 times less copies. Pure numbers not always relevant, effective demand (i.e. number of people who actually buy at given price point) also plays important role.
3. Financially it makes a perfect sense to omit 20% sales to PC market immediately and delay it for 1-2 years on exclusivity deal. Company saves costs, get benefits from platform holder and loose almost nothing as it will get tail sales on PC anyway.
This is why it was a practice with long history.