They always saw themselves ad the kingmaker and presented themselves as a liberal alternative to the other parties. Although effectively they forgot about everything liberal besides their economic policies as soon as they got into power.

Effectively they and the CDU/CSU were symbiotes of one another. The CDU always could pretend to be more conservative on economic things and then drop this for their FDP partners, while the FDP by sheer necessity had to drop all their topics besides market-liberalism.

This worked, and I think people knew that if you voted FDP you would get CDU politics anyway, but you could say you didn't vote for them.

And I mean, the last time FDP went into a coalition with someone besides the CDU/CSU they basically acted as fifth columnists.