Why was there no issue with the Tu-144 flying above land?
The actual 'legal' reasons have already been mentioned. However, there was a bit more to it.

Tu-144 was meant to fly over land from the beginning; there was no way around it, unlike Concorde. So it was designed to fly higher. In particular, Tu-144 had about 20% lower wing loading and 20% higher thrust-to-weight ratio (at MTOW) than Concorde. (The reality was a bit more complicated; for example, Concorde was limited to FL600 again for 'legal' reasons, due to certification of the pressurisation system AFAIK).
Soviet citizens, apart from not being asked their opinion, were quite used to sonic booms from military aircraft. In many places of the country, they wouldn't even raise an eyebrow. In the Urals where I grew up, I heard them almost daily.