If it’s about money – it’s usually the Premier League’s fault.
West Ham were the club mainly linked with Muriel with claims in both the Italian and English media of offers being pending, Everton were linked because of the assumption they needed to add more upfront given what was then a likely transfer of Romelu Lukaku.
Sevilla have agreed a fee of €20m, a record signing for them, and will have to pay Sampdoria 20% of a future transfer fee. Those figures are less than what was mentioned when Everton and West Ham were linked with the player.
There’s a distinct possibility that neither Everton or West Ham were actually seriously interested, in which case it’s the media who would have upped the player’s price rather than the clubs.