Inheritance laws in The Netherlands mean that everything gets split between all the children and things don't go in bulk to one heir or heiress. It also explains why we don't have (many) grand estates or castles.

Another reason is that much of the nobility died during the 80 year war and in the following wars in the 17th and 18th century. As we were a Republic no new noble titles were created. That only started after 1806 when Louis Napoleon became King of Holland and in 1813 when Willem I became first Sovereign Prince and in 1814 King of the Netherlands.
In the 1980's it was decided that new noble titles will only be created for members of the Royal House.

We still have several noble families but they are not all very wealthy. In the Netherlands the title of count (earl) is basically the highest title, than there are barons, knights and jonkheren. yes there are a few higher titles but they belong to families who were incorporated into the Dutch nobility.

Next to the noble families we have the Patrician families. Some of those still are very well off. But the richest layers of Dutch society are to be found among entrepreneurs. The heirs of the Heineken conglomerate or the Brenninkmeijers (one married HRH princess Maria Carolina de Bourbon de Parme).