Bitcoins can exist without exchanges, but would you support the argument that the existence of exchanges are among the factors facilitating the popularity and accessibility that people have to bitcoins?
Exchanges play an important role in the encryption field. Its existence makes it easier to buy and sell cryptocurrencies, promotes more investors or traders to buy and sell bitcoins, increases people's demand and popularity for bitcoins, and expands market.
It can also help certain currencies gain popularity. Many investors will choose potential currency investments based on transaction volume.