Because they do so much work upfront for you. I worked in algorithmic trading for a bit over 10 years but left in 2014. I spent a few months in my spare time bu

Because they do so much work upfront for you. I worked in algorithmic trading for a bit over 10 years but left in 2014. I spent a few months in my spare time building out a trading and backtesting platform, pulling data off of yahoo finance, connecting to Interactive Brokers via their C++ API, etc. It was all very slow and tedious, and during my googling one day, I come across quantopian. I felt like an idiot- they already had free access to morningstar with a decent API around it, tons of other datasets you could subscribe to, and a fully fleshed out backtesting platform with risk measures, pretty graphs, etc. It would have taken me months-years to get to that point. Shortly after they also included integrations to IB and Robinhood so you could very easily take your ideas and actually live trade them. I immediately stopped development on my trading platform and just started using Q's. Q could potentially take my algorithm and start using it themselves, though they actually put money into algorithms they think are promising and share the profits with you. That's a small risk IMHO. Hackers and the like... I did this stuff for 10+ years. People WAY over estimate the value of this code- you have an idea, you backtest, hope it works, and then you put it in the wild. I have never seen an algo that is a real guaranteed money maker (aside from arbitrage/hft stuff). What are these hackers going to do when they take a 10% loss one month and don't understand why? Some "signals" can be used in-line fairly generically with other algorithms to enhance their performance, but I will still bet on the guy that knows/understands the algorithms to not lose his shirt, then some hacker dude that likely has no capital to begin with and may not even understand the basics of financial markets. One thing you seem to overlook is that it is one thing to go buy a bunch of historical data off ebay, but you need to constantly update that if you are going to live trade- Q handles that part as well. If I was looking to make a business out of this, I would build my own platform. But using it as a research platform to invest my own money, Quantopian is awesome.