Why the Apple ecosystem argument holds in Oman specifically
Two verifiable reasons, beyond the general one about devices working together.
Apple Pay works in Oman with Ahli Bank, American Express, Bank Dhofar, Bank Muscat, Bank Nizwa, Meethaq, National Bank of Oman, Oman Arab Bank, OMpay and Sohar International. That is a wide list. By comparison, Google Wallet tap-to-pay in Oman is currently limited to Ahlibank, Sohar International and Sohar Islamic. If paying by phone at a card terminal matters to you and you do not bank with those three, iPhone is currently the platform that supports it here.
And Apple lists Oman among the regions where the Apple Watch ECG app, irregular rhythm notifications and hypertension notifications are available on supported models - which is not true of every country.
Those are specific, checkable advantages rather than a general claim that one platform is better than another.