Best answer by Hikari
Dual SIM phones are more popular in emerging markets like India, Brasil or Poland. This is where manufacturers put their focus on releasing new dual SIM phones. British market is treated by phone makers like Samsung or Apple as developed one which means they put more focus on releasing flagship devices (best camera, premium design, top specsheet) rather than dual SIM versions. Good news is that likes of Xiaomi, Huawei and Oppo are joining the battle for customer and this may bring in the future more options to choose from and force Samsung and other big player to reconsider their strategy.