As to why you can’t get a loan – I’m sure this was said, and in skimming the replies I didn’t notice if anyone said the secondary market for Jumbos is gone.
Lending was great when you could slice loans up to sell to some “investor” reaping all the profits up front before a single payment was made, but not anymore.
All I can say is be patient. If you’re 30 yrs old, debt free, and making $250+/yr you should be able to put more than 10% down. Heck, you should be able to buy the house outright in 5yrs or less.