I supppose because it would cost more time and money to build an alternative of the same quality from scratch?
Seriously though, three people was working on that site almost full time for more than a year now. That's about 600-650 workdays. A decent junior developer (the cheapest programmer who could possibly do it) earns at least $200 a day. That's $120000 worth of wages. Which means, you will have to use this software for more than 10 years to justify writing an alternative, and we haven't even considered any additional future development.
Seriously though, three people was working on that site almost full time for more than a year now. That's about 600-650 workdays. A decent junior developer (the cheapest programmer who could possibly do it) earns at least $200 a day. That's $120000 worth of wages. Which means, you will have to use this software for more than 10 years to justify writing an alternative, and we haven't even considered any additional future development.