747 first flight was in 1969. 737 first flight was in 1967. Both B-52 and Tu-95 first flights were in 1952, both still in service today. Sometimes problem is

747 first flight was in 1969. 737 first flight was in 1967. Both B-52 and Tu-95 first flights were in 1952, both still in service today. Sometimes problem is solved, and there is no need to solve it again, it would be insane for Russia to abandon Soyuz and develop something new at huge cost.