My guess would be that the speaker has never had any one even comment to them about their pronunciation. Even the, if that's the pronunciation they have heard and used for years, changing would require constant focus.
Where is constant correctness in language a requirement? Definitely not here on these Forums where we all, me included, have a chance to edit before we post, and I still see lapses every day. I see them, but the only ones I actually care about are those I make myself.