According to Psychology today, fear is a vital response to physical and emotional danger that has been pivotal throughout human evolution. So what were the Israelites fearful of? Not having a leader? Feeling that they were alone or being abandoned?
It's not so out of the ordinary that they went back to old habits at a time of fear. Although the Ramban and Ibn Ezra go out of their way to point out that the Jews were not interested in worshipping idols, it's not strange to think that they were. They had just spent hundreds of years in slavery in a place surrounded by idolatry. All of a sudden God saves the Jews, there's a pinnacle moment at Mt. Sinai and then silence. Working with people in addiction recovery, this is a common thread. People spend their entire lives battling addiction until finally having a Mt. Sinai moment and getting sober, but then something happens which causes an inordinate amount of stress and they go back to their old habits.
Even though the addictive substance is self-destructive and hasn't shown any success in the past, it is where they go. Ultimately one needs to pick up and continue rather than allow one enormous misstep to define the rest of their life. As Hesse states in Narcissus and Goldmund, "There is no peace ... that lives within us constantly and never leaves us. There is only the peace that must be won again and again, each new day of our lives..."