Without reading the above posts other than the first post:

1) Accrued value
They have furniture, tables, lamps, paintings, statues, beds, and other non-taxable goods in plenty, therefore they are satisified with their status quo. Tell them they have to house homeless in their villas and they will never agree, tell them you plan to tax total worth and they will never agree. Tell them you plan to tax income and they will not bat an eyelash.

2) Tax loopholes
If you buy municipal bonds they are taxed differently than if you buy stocks or a company. The derived income from them is also taxed differently. There are places where you can place money tax free and get a very ultra low compensation rate for it compared to other methods. Since they were taxed at the lower rates as they earned it, they now can 'hide it' from further heavy taxation where people who would climb up do not have that luxury, to whit they simply cannot put enough cash into these things to pay for their needs as of yet... but the super rich can.

3) Avenues of escape
If the pressure really grows they can take their money, open a business in another nation, and leave our nation. There are plenty of nations which would be happy to have a billion dollars flow into their economy.

4) Write Offs
The poor man does few things which can be written off from taxation, but the rich have many ways to write off a lot of income. I personally know a man who puts $140,000 in his bank annually but pays taxes on only $3000 of it. All of his actions are legal under the current tax code.

5) Easier to take the loss of income
To a rich person deciding between (I cant help it) a Jaguar and a Porsche the  ability to buy a car half the cost is there. But to a poor person buying half a geo metro is not an option. Yes they will hate driving a mere BMW, but they can suffice they think.

6) Passing the buck along...
This is the most damaging, but will be the most commonly used method also. The rich do not pay their taxes if they have a business. The buyers of their products pay their taxes. If prices must be raised due to taxation, and cost cutting methods must be done, so be it. The quality control on the common ketchup may drop, and the price may grow 50%, but there you go... your still buying the ketchup. Because all the prices likewise grew and this is still fairly cheap (In relative terms)

7) Sneaky buying
And last, but not least, they can buy elsewhere. Just ask the US Yacht making business what happened when the Luxury Tax was installed. Oh wait you probably cannot find a US Yacht making business anymore... despite our being the best makers, and the ones with the most highest production rates, of Yachts. The buyers just went out of the US for their Yachts to avoid the taxes and likewise huge price increase on US Yachts. They can buy anything they need elsewhere and they know it. I dare you to try to get pineapples at a reasonable price if they are taxed 100%, where those in the know can bring in a certain amount per a day, and sell it on the sly to those willing to pay a fee equal to 20% of the cost of the pineapples, instead of 100%.