Same can be asked, why do some like lock-in so much that they avoid cross platform development?
But what I have seen are very confident web frontend devs (and product managers too) who only consider web solutions, and dismiss native apps as being duplicated work.
It's worse than duplicated work, it's duplicated different work.
And if you do everything right, both app experiences will be mostly the same.
In my experience the backend of most non-tech and some tech businesses is a database and some trivial validation rules. Everything important is in the design of how the data is displayed on the front end.