The interest rates often make those unattractive. You also expose yourself to the risk of a margin call with its many implications. It isn’t something the average person should be doing casually.
Most other brokers, even Schwab and Fidelity, will not.
Agree it's probably not a good idea for most people. (I might argue the same for a heloc, depending on what for, what emergency savings, what level of job security, etc)
FWIW my brokerage gives me a margin loan at 4.9% up to 30% of the portfolio. The interest is literally lower than the mortgages I see advertised these days.