There are many SSO's for all the times of the day, most SSO's are not permantly in sunlight.
The comment I replied to implied that any old SSO would have the property of being always in the sunlight, this isn't true.
The particular issue with a terminator SSO is that region will get crowded (sure, space is large) and one collision will seed debris to spoil it for everyone for some time.
> Riding the terminator is useful for active radar satellites ..
All sats need some level of power or another, not all want to ride the terminator, see (for one example)
https://modis.gsfc.nasa.gov/about/
in which different sats in the constellation travel at different times of day (why?).