Why are MOSFETs mostly preferred than IGBTs in DC DC converters?

Selecting a MOSFET/IGBT is based on your application.

Consider you have a converter circuit with lot of noise filters. To reduce inductor and capacitor sizes, you have to increase frequency. Now, if the converter is operating at higher frequency, say 100Khz, MOSFET is your option. Becuse it has a very good switching speed compared to IGBT.

Now, take a different application with high current requirement and lower frequency. Here the importance is biased to on state resistance of switch. Comparatively igbt has lower resistance which makes it the better choice.

So that's how we are selecting switches.