...While also making it more resistant to differential cryptanalysis (called DCA from now on). DES died because of the small keyspace. Without the NSA/NBS changes it would have been insecure from the start and would have been a lot easier to crack once DCA was out in public.
The changes proposed made DES harder to crack for the NSA, but less "future safe" once computational power caught up. I don't know enough about DCA to know whether DCA-weak-DES could have been made safer with something like 3des, but I wouldn't want to bet on it.
NBS became NIST and they still have credibility to you. Whatever reason you come up with why it was okay back then also applies today.
[1] https://en.m.wikipedia.org/wiki/Data_Encryption_Standard