"Es gibt" = present tense for "There is/There are..."
Inversion: "Gibt es...?" (Is there.../Are there...?)
"Es gab" = präteritum (imperfekt) for "There was/ There were...?"
Inversion: "Gab es...?" (Was there/ Were there...)
Hence the translation: "Was there a lot of traffic?"
I was told not to use the simple past tense in German because most people don't use it anymore, is that true?
I was told that the present perfect is actually used more frequently, maybe because it expresses recent things and experiences, but of course the simple past is also (as in English).
It depends. Some dialects have indeed completely lost the simple past tense.
In the standard language, however, it still sees some use (how much depends partly on the region - I think the north uses it a bit more than the south).
As a rule of thumb, very common verbs such as sein, haben, werden are more likely to tolerate or sometimes even "demand" the simple past.