Sometimes the toy idea comes first and the show comes second. And if they go to the trouble of making the toys in the first place, that's a serious investment as making the pipeline for their production is very expensive.

So if the toy tanks, that's a lot of wasted money, and the show could be replaced by one that both gets good viewership and also sells toys, and that's the real goal. If the network never bothered with merch and the show did well, then that might be fine, but it will still be preferable to replace it with something that can sell toys. More revenue streams per idea is better, and at the end of the day these people are out to make money for their investors, not good TV.