Not only are they making less money on the sale, but they face higher costs even just getting the car to the UK, meaning that the effective margin on the international is even lower.
Pure uninformed speculation, but it seems to me like its about sales pipeline and leveraging momentum. It doesn't make sense for them to fully pump the US dry before then expanding into other major international markets. You want to be entering a new large market on an upswing, not on a downswing. Also, waiting would give a lot of space for other international automakers to catch up in their local markets, since people are increasingly interested in buying EVs today
Restricted supply of hot product leads to greater demand and froth... see Tickle me Elmo, early model iPhones, etc. Hype is gold for new products.
Markets that never get demand met will eventually wither as alternatives arrive and resentment grows.
Establish distribution channels early at low volumes, fix the bugs, then scale at maximum profitability.