PR does not have to be renewed as often as a work visa or spouse visa.
PR gives you better credit at banks, in many cases anyway, so if you want to build a house, there you go!
If you're asking about why wait 10 years, however, that could be so varied an answer. Some people may have come and gone from the country, thus not having a continuous residency here (and therefore may have thought that affected their application). Some people may simply have not had a spouse visa for 10 years, but instead may have had 1-year work visa renewals or something like that. Yes, immigration seems to prefer that if you are married to a Japanese, that you keep the spouse visa for at least one 3-year period, but it's not a fixed immigration policy. Makes sense that they would want to see some proof like that to suggest you are serious about staying together. Lots of "marriages of convenience", you know.
I was here for 3 years on work visa, got married and therefore got a spousal visa, but it was only for 1 year at a time, so after 3 or 4 more years I applied for PR at the same time I renewed my spousal visa. I guess I was lucky in that I got my PR only 2 and a half months later. Some people wait far longer. As they say, your mileage may vary.
