Second, it's likely the high cost of financing (typical of non-cash, first-time buyers). All the closing and financing costs add up quick. Suddenly, property taxes and HOA dues become very real expenses when they need to be pre-paid.
Third, it's definitely the large initial cost of transitioning into a new home. With a brand new home, there's landscaping and basic window treatments necessary, as Chris mentioned. With a pre-owned home, there's lots of cleaning and maintenance items that start from the day you move in and never seem to end.
But, the privilege of customizing a home to exactly how you want it just makes all the trouble and expense feel worthwhile.