Reversing vowel sounds

One for Henry Higgins. A lot of people from the rural areas in my country have a habit reversing the sounds of their o’s with their u’s, and also the ‘e’ with the ‘i.’ They do this, whether in their provincial dialect, or using the national lingua franca, or even English.

What could possibly be the reason for this?

“Dey say yoh pawn sambadeh noh…
Bat ay don’t want nowan bat yoh…
How can yoh leb wedawt regriiiit…
Am ay dat esi to porgiiit…”