I think it's mainly not mixing with native English speakers and lack of will to improve, lack of will to put in the work.Lol , they can’t fix their accent even if they want to ..
According to a study I read years ago about why some immigrants accent doesn’t improve even after spending years at the country. The main reason is they didn’t go to school, college or uni. Also they don’t travel enough and mix with local people , my god it’s like the study was made about them..
1/No college or uni degree.
2/Traveling to the same place over and over.
3/No Brit friends.
Now WALK with your head down ..
My grandma is Spanish and she never went to school, didn't learn to read or write yet she made the decision when she came in France to mix in with the French parents and neighbours, she didn't want to stay as the 'Spanish immigrant' for everyone. Now she's proudly Spanish and French Meme will never understand what it means to integrate yourself in a culture. The Cunts are disrespectful to any culture.
What a sad life, they have no tradition, no real home, no humor, no real friends...