Your technocrats may be noble, but they are also human. Give them enough power and they will swiftly lose their nobility.
There's a corollary here.
I think a probably-more-precise description is that corruption isn't just caused by the presence of power, it's the result of the disparity between power and wisdom.
If you increase power without increasing wisdom, you'll see more corruption. If you have absolute power, you probably don't also have absolute wisdom (if such a thing is even conceptually possible).
There's a second corollary here: Power doesn't only corrupt the one that wields it. Its mere presence can sour others. (Envy, greed, etc.)
In a similar vein, people also love to say that knowledge is power, but I think "information asymmetry" fits better.
(Also, power is inherently temporary.)
Was this because:
A. They never liked your "lame jokes" in the first place and were
behaving without integrity in the past?
B. The politics got to them and they ceased to enjoy the finer things in life?
It's very likely you've got anecdotes that would support A over B, but as an outsider, I'm cautious to assume. :)