That‘s probably what they thought, too. If you just pick a random bilingual person and let them proofread your learning material you are going to end up with crappy learning materials.

If you want good content, you need good editors, and they are neither cheap, nor easy to find.

The reason why companies try to save money with editors is that they don‘t „scale“ (one dev and a designer can program an interface that can be used for 20.000 different questions, but you need a lot of people to come up with those questions)