The 33-year-old has been allowed to leave, and former Hammer Hartson is not surprised.
The midfielder departed the club on Thursday by mutual consent, after four years in which he made 157 appearances and scored 31 goals for the side.
He has become an increasingly bit-part player in the last few seasons, and that has become an even bigger problem this term, with manager Bilic having brought in a number of new faces as he seeks to change how the Hammers play.
And Hartson has suggested that the tweaking in approach at the Boleyn Ground is the reason behind Nolan's departure.
“I see Kevin Nolan has left West Ham,” he wrote on Kicca.
“There is always player movement when a new manager comes in. Slaven Bilic clearly wants to play a different style of football than big Sam. Nolan was a player under Sam that broke into the box and fed off a big man and got goals - mainly off Andy Carroll. And he did it well.”
It is a fair assessment that Nolan has been allowed to leave West Ham because he doesn’t fit into their new style of play.
The Hammers fan base became increasingly aggravated with what was on offer under Sam Allardyce, and Nolan is arguably the epitome of that style of football, with his robust style being a direct contradiction of what Bilic is trying to get out of his side.
Given that the Croatian has spent so heavily to bring in more technically gifted players like Dimitri Payet this summer, Nolan’s exit probably doesn't come as the biggest of surprises.