So, there's a couple things going on here. One, he is most likely being scapegoated for the flash crash. It is highly unlikely that he alone caused the market to crash.
However, he absolutely was spoofing trades. That is not a high-speed activity, and can easily be done by point-and-click traders. There have been any other traders that have been known to spoof as well. His problem, however, was that he was dumb about it.
The law is about intent. When your order was placed, it must have been placed in good faith, with the intention of getting filled at the time of entry. However, it is completely okay to decide 10 milliseconds later that you no longer want to get filled (for example, you realize the market is moving against you.)
The problem here is that intention is extremely difficult to prove. You could say "I have a machine learning model that said it was a good price to buy when I placed the order and a second later, it changed the price". So, even if it is generally accepted that a trader is spoofing, the burden of proof lies on the prosecutor, and its a fairly high burden.
Sarao made it very easy, because he wrote in emails, exactly what he was doing, that he wanted a special order type that would never get filled. Then, the manner in which he placed those orders was obviously meant to drive fills into other opposing orders, and once those got filled, he would cancel the initial "fake" orders.
He also did a number of other things, and most importantly, wrote down what he was doing to make it easy for prosecutors.
I highly recommend reading the indictment:
https://www.justice.gov/sites/default/files/opa/press-releas...
It explains everything that he did and the evidence against him.
Overall, the flash crash blame is the media/officials finding someone to blame, but he did commit a crime, and that's why he's being prosecuted.
The reason others are not being prosecuted is because others aren't stupid enough to write down their crimes.