We are nowhere near as big a club as both of those. both spent hundreds of millions (Everton 450 million in two summers) and pay over 100 k a week ( West ham)
if they offered him the money he would want to go. Simple as that.
If he keeps his form I could see him going to a club like Everton / west Ham for 30 mil next summer. If he has 2 wonderful seasons with us then Arsenal / Spurs for whatever the silly price is at the time.