You misunderstand a lot about what went on there.
One, there is no question that Sarao had nothing to do with the flash crash. The cause of the flash crash was a fund manager adding an extra zero to a trade they were making. The reason Sarao was blamed was to put pressure on him, and because the SEC needed to blame someone for there total failure to properly manage markets (the person who prosecuted the case against Sarao was the person responsible for monitoring electronic trading, she built a huge media profile through this case...no-one ever asked why the only person they charged for this was a disabled guy working out of his parent's bedroom).
Two, Sarao did go to jail in the US and the UK. This in itself was pretty unusual because he admitted to the crime, the crime had never been charged criminally, he explained to prosecutors exactly what he was doing, and he had relatively severe mental health problems which (given that he was totally compliant with prosecutors) should have meant he was never extradited (I believe he was in jail in Chicago, and he became very unwell whilst there). He was extradited to the US because prosecutors wanted to see him suffer (this is also why their first contact was a dawn raid on his parent's house), and it worked because he ended up signing a plea deal for something that he was very unlikely to actually get found guilty for (the case went on for something like 10 years).
Three, the reason why Sarao was charged was because people at HFT firms were losing money due to spoofing. That was it. The person who notified the SEC worked at an HFT firm. Ironically, Sarao himself also attempted to notify the SEC about things HFT firms were doing...nothing happened with that.
Four, people have been spoofing for decades. When markets were still a mix of open outcry and electronic, the largest traders were all spoofers. Saying that spoofing is illegal relies on the notion that once you enter an order, you must have the intention of trading at that price...do you know how to measure intention? The practice was only made illegal when the market went full electronic, and the order book data was being used by HFT firms.
Five, the reason why Sarao didn't go to jail was because the case against him made no sense. He was spoofing, spoofing is illegal but when the SEC raided him (again, highly unusual) he thought that the SEC was actually investigating his previous communications about HFT firms...it wasn't. He gave huge amounts of information to prosecutors about what large firms were doing, apparently he sat them down and went through hours of examples of market manipulation...no cases were brought as a result of this.
Sarao is the archetypal of example who was forced to serve real time at the behest of HFT firms in order to further political aims.