Because that'snot what the graph claims, and it is definitely not what the graph implies.

The graph says that there has been a 400% increase in the prevalence of autism. That's not true, and is unsupported by the evidence. There has been a marked increase in the effective diagnosis and therapeutic interventions, but autism was largely undiagnosed and under-reported for almost all of human history. We're still improving and refining the diagnostic criteria, and any changes in the number of cases should not be suggested to support any causal relationship with anything.

The graph is a lie, intended to push a political narrative that undermines the credibility of actual science, all in a transparent effort to distract from powerful child rapists raping children.

The rate is higher because we can "catch" more cases with better diagnosis.

Imagine machine that is throwing 100 balls per second. Another machine that can catch 10 balls per second. You catch 10 balls.

Now newer machine can catch 20, and newer can catch 50.

Does that mean the number of thrown balls is higher? No. It just means we have machines better at caching them. The same goes for any illness, autism, schizophrenia, cancer, depression...

Some ilnesses we are better at curing, does that mean the the illness is getting weaker?