The red squiggly line merely means the word isn't in the dictionary used by the app. It has nothing to say about grammar, which is the real problem. There are grammar checkers, but they generally suck from what I have seen. One would think though, that the lose/loose, too/to/two errors are so incredibly common that every use of the words would be flagged for a quick double-check. I know I've made errors like that before, even though I know better. If I proof, I usually catch it. I do not know what 'editors' do these days, it is quite apparent that they never read the articles. Kinda like us here on FR!
In the old school days, a copy editor would do the proof reading and catch the grammar errors. Now it’s no red squiggly and publish.