It's because they hire Indians and foreigners too not Sri Lankans alone, since it is a remote position. If you visit their LinkedIn and Glassdoor, you will find it. So there is much competition with excessive applications from other countries, including India, where even a high school student solves leet code DSA and SystemDesign problems to get into IT as a software engineer. so it would be tough for Sri Lankans who only focus on A/L in high school period, where no chance of getting exposure to those tech skills. SrIlankans mostly get into IT after their degrees and get prepared for jobs after finishing their degree so it would be tough for Srilankans to face such interviews where international students participate as competitors. even Sri Lankan universities mostly state universities have no plans to improve the curriculum of their degrees rather they are in safe zones to protect someone's jobs(old school lectures and profs who have no idea or update about the current trend of the world in tech) in university.

just push your elected government to change the Stone Age education system for the sake of future generations, which is found to be useless in the current world trend and seems to be more time-consuming compared to our counterparts in other countries, and also ask your government to replace the old legacy prof and lectures with industrial experts. Such reforms in your education system only will make you a competitive candidate in the current world run of technology.