They are targeting their market. I know it's a gross generalisation, but you'll get the loan consolidation people advertising on daytime TV to people who are at home because they don't work, and you'll get stairlift companies advertising around programmes that have a large number of elderly viewers.
It would make little sense to advertise a stairlift during Hollyoaks, for example, but probably more sense to do it during Corrie, but the rates for prime time advertising would outweigh any gain in sales. So they do it during daytime TV. They know that the great unemployed mass are sitting there along with the pensioners.