Disadvantages of DLL clock generators compared to PLL
There are a number of disadvantages to DLLs. The four I can think of right now:

The delay though each element is often highly temperature dependent, which means the number of delay elements changes as the temperature changes. As each delay is a discrete time step, this can cause significant jitter and phase noise.

This effect can also mean that the DLL is unusable over a wide temperature range as the part can literally run out of delay elements or have insufficient (depending on which extreme of temperature you are at).

The delay through each element is not the same and has a stochastic mismatch and therefore jitter can result.

They can struggle with a varying reference input (so we cannot use spread spectrum sources with them).

They were, the last time I used them, unsuitable for fractional N synthesis.


Excellent source at this paper.
DLLs have got better over the years, but they are usually unsuitable if you need a high purity output signal or want to use spread spectrum for EMI control reasons.