He's probably very happy being number one at a fairly high ranking league one team, why go elsewhere at this moment and lose what is a given here?
There will be a new contract on the table soon and as long as its a hefty hike on his current contract we could see him here for maybe another three years.
Because he could get at least 10x his current salary elsewhere, take a massive step on his career ladder, and if he’s really really ambitious and hopeful… there’s a tiny outside chance he could go to a World Cup if he goes to a PL side and impresses in the first half of the season.
A football career is short and injury/bad form could end it any time. You have to take these opportunities, and frankly Argyle have to take it with his contract length ensuring a good fee.