I noticed that *Cj/*Cy (depending on if one uses IPA or IEist notation) and *Cw sequences are rare in PIE (with most being the result of schwebeablaut or regular ablaut). Among sequences that aren't the result of schwebeablaut or regular ablaut, *Tw sequences are the most abundant (with *T denoting any dental, including *s), followed by *Kw (*K denoting any dorsal), then by *Hw (*H denoting any laryngeal). The sequences with *j/*y are even rarer, with the same T>K>H pattern as sequences with *w. *C is never a labial or a resonant. Even the *Tw sequence represents a very tiny portion of reconstructed PIE. Any reason why C+glide sequences are rare and why the dentals are the most likely to be *C in both *Cj/*Cy and *Cw while *C is never a labial or resonant in such sequences?
Edit: there are also *Cj/*Cy and *Cw arising from combinations of different roots and elements. The above doesn't refer to clusters of such origin.