The way someone types on the internet is not necessarily reflective of their actual spelling ability. In that sentence alone I've had to go back and correct several typos caused by fat fingers on a small keypad. Some are autoincorrects
Others use text speak or slang because it's quicker.
Home educated children don't learn solely from their parents. Some take classes, some use tutors and most home edders are active in their community, learning about the 'real world' by being in it. A big part of home edding is not teaching in the waybthat a school teacher might, but rather facilitating, providing opportunities and fostering a love of learning. Both myself and my sister went to (the same) school, I am fairly good at spelling and grammar, she isn't. I love to read and devoured hundreds of books as a child whereas my sister wasnt a big reader, and i'm pretty sure that's what made the difference. If a parent strives to create a literacy rich environment and foster a love of reading then their child is likely to have good literacy skills regardless of how literate the parent is.
Studies of outcomes for home educated children have found that what is important isn't the parent's level of education but rather their level of commitment. A lot of parents of home educated children did not go on to higher education yet that doesn't seem to have stopped their children from doing so.
From a study by Paula Rothermel:
'In this study, parental level of education did not limit the children's attainment. At least 38% of parents in this study had been educated at comprehensive schools and at least 21% had no post-school qualifications. Whilst 47.5% of parents had attended university, at least 27.7% of parents in the study had not.
Common to all families involved was their flexible approach to education and the high level of parental attention received by the children. Children benefited from the freedom to develop their skills at their own speed. Thus, parental input and commitment, regardless of their socio-economic group and level of education, may be the most important factor in children's development and progress.'
pjrothermel.com/Research/Researchpaper/BERAworkingpaper.htm
Besides, let's not forget where these parents got their own poor spelling from - I'm guessing most of them went to school
Perhaps they don't want to put their own children into the same system which they feel failed them.