It probably does cost Google something. They scan apps and devices for malware, and anything that increases the number of apps and ways to distribute them will increase the cost. They also have to certify these app stores, they aren't just going to let anyone set one up and start distributing malware or pirate streaming apps.
It feels calibrated to deter unserious applicants, but not cause further legal woes.
The real issue is F-Droid and similar open source app stores. It remains to be seen exactly how it is going to pan out.