This is a common misperception. Lesser charges were included; Casey Anthony could have been convicted of second degree murder or manslaughter. That case was a travesty, was handled badly by the judge IMO, and the jury did not do their job. If this link works, it's a copy of the jury instructions, which are very clear.
https://www.google.com/url?sa=t&sou...Vaw2dwOOcZ1-Q4L6rNNbu7JSk&cshid=1577658313716
The cases I've watched (in multiple states) have been consistent in including lesser charges, and I have the impression that is more common than not.
I don't think the prosecution will have any trouble getting a conviction in this case. I can't imagine what kind of case the defense could present.