They do both involve taking risks for money admittedly but there are crucial differences.
You actually participate meaningfully in the outcome via investing instead of just price discovery and the successes are derived from the valuation or income of the venture instead of the losers. The participation is not only in impact on their credit rating and sales but also concrete choices in government of it.
Not to mention in principle there is an actual activity being backed by the investment to produce non-zero sum gains. While there may be risks involved in say, running a turnip farm or sending a ship across the ocean, you are still supporting a useful activity for its own end. Crucially as well there is motivation to do the task even without the market, even though it may enable it.
If you can manipulate the outcome of the turnip farm (as opposed to the market) to make it succeed that is doing useful work and not just cheating a bet. A guideline of the distinction would be - would charging somebody for making the outcome successful in a not otherwise criminal way be a Kafkaesque injustice?
You can in fact use the market to gamble via options intended for credit or insurance but stopping those by stopping the market entirely would be throwing out the baby with the bathwater.