Was MakeMKV ever claimed to be open source?
Not sure if it's exactly what you want but I've used MKVtoolnix in the past for .mkv operations, worked fine for me. And ffmpeg also works great for general audio/video stuff though I've never tried bluray -> .mkv with it.
Kind of seems like an ad, every link to their site has a referral in it ( /?ref=news.itsfoss.com ), guessing itsfoss gets paid for those clicks.