Stocks is a popular asset class even among brokers who normally refer to themselves as forex brokers. These brokers first started offering stocks when contracts-for-difference (CFDs) became a common way to trade different assets for retail traders. For the first time, traders then got opportunity to trade stocks from all around the world without having to sign up with stock brokers in the various countries.
Stock CFDs have also made it incredibly easy to make money from falling stock prices by shorting, which could be a complicated process in the traditional stock market. All in all, stock CFDs have become very popular, and nearly all forex brokers now offer stocks of at least a few major companies.