The OP has a very good question.
In my experience, people who own diras have them bought by parents/in law or use wedding present money for a downpayment, and then pay mortgage instead of rent.
I had neither of these luxuries, (18 years ago 1998-2000) and lived in a top floor apartment in Kiryat Sefer (or Qiryat Sefer ;)) forjust under two years. When the money ran out, we moved back to England. We moved to Gateshead, which is the cheapest kehilla to live in. I was able to teach in a yeshiva ketana for just over a year, when I had to go get a proper job.
But I realise for many they don’t have anywhere to move back to, or can’t go to work for various reasons, and this becomes a major problem. I don’t see how, b’derech hateva, a kollel family can live on a regular kollel stipend, without any supplementary income. This could be a property investment on their behalf, or something like giving extra lessons to local schoolchildren.