Talad and Laanx found small cave under the Azure Sun. They enlargened it a lot. if there were any stalactites, they probably were broken in the process and if there were any, for sure not close to the walls of the actual Yliakum cave. Interesting, isn't it? Especially that stalactites form thousands of years. And how big stalactites we see all around?
I explain it by it that eighter Laanx and Talad waited so long, before they started making the place habitable (soil, oxygen and stuff). Or they used powerfull spells, bending the time as they wanted. That's rather important aspect in the Yliakum creation.
As to answer why the heck the stalactites don't grow anymore.
You know, for stalactite to grow, not only time, and properly mineralized water is needed. You need special microclimate! For example, wind and changing temperature kills stalactite growth and turns them into "dead" forever. So all stalactites in Yliakum are "dead". Of course i'm not talking about smaller caves somewhere.