There are countless types of equity funds because there are many different types of equities.
Here, the conjunction because is used to introduce the reason why there are so many types of equity funds.
Because there are countless types of bonds, there are a whole array of bond funds depending on what they invest in.
Here, the conjunction is mentioned at the start so a comma is need when the independent clause starts. Also, the independent clause after Because answers the question why are there so many bond funds depending on what they invest in?