Because it serves multiple purposes for him with near zero downside:
It gets him out of here and to the team of his choosing all along - L.A.
It's on record that he never wanted to be here, despite the reunion with Jarvis.
It's on record that he tried to get out the moment he got here and never stopped trying.
He knew there was zero chance of him getting traded for given his contract and his high-profile and perceived value, so he needed to get released and he knew he could absolutely never get released if he did what he can do so effortlessly.
If he caught everything that came his way like he can, and is once again showing, his value would FAR exceed any little bit of outside drama his cohorts could cook up on TweetFace, thus doubling down on him not being traded for OR being released outright.
Diminishing his value on the field by just going through the motions was his ONLY play to get where he wanted, and yes, to your point, I think his "frustration and lack of being used effectively here" completely fed into that, even though his own actions fed THAT. A snake eating its tail.
Once released, taking a one year deal gets him to the open market while riding high in an Air Raid offense all while being in glitzy, glammy Los Angeles with the paparazzi crowd he covets.
I'm not saying that this is definitely how it went down, BUT, I am saying that it would be a very hard sell to 100% convince me it wasn't.
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