Photos is a great app and has universal appeal - powerful, intuitive editing, easy and smart search, free backup, etc.
Snapseed is also one of the best mobile photo editing tools around, certainly the best free one IMHO.
My guess is they used the Nik technology in these tools to make the editing and retouching functions work so well, and now they sold it with contingent that they can use it in perpetuity...
Here is the weird part -why wouldn't Google merge Snapseed editing with Photos? It would be a killer combination and dominate the consumer space, locking in users to the Goole platform. Isn't that ultimately what they want?.
I always assumed Snapseed and Photos would merge one day. Yet, it has never come, and instead Google is empowering others in the space with their tech.
Maybe they have "good enough" dominance in the area and don't care anymore? Maybe all they care about is tying users into the Drive platform and Photos is just another funnel that did good enough and can be ignored?