This is because the reaction occurs by SNI mechanism. The formation of products is governed by the stability of the carbocation formed from the cleavage of C–O bond in the protonated ether (oxonium ion). Since tert-butyl carbocation [(CH3)3C+] is more stable than the methyl carbocation CH3+ Therefore, cleavage of C – O bond gives a more stable carbocation [(CH3)3C+] and methanol as products. Then iodide ion (I−) attacks tert-butyl carbocation to formtert-butyl iodide.