Have a look at the following diagram:
This shows measurements of the CMB by various experiments, with multipole moment $l$ on the x-axis and the temperature of the corresponding moment on the y-axis. (Please correct me if I have that wrong.)
Looking at the plot, I can see that WMAP's results extend to about $l=1000$, and they become poor as we go to higher values of $l$. Meanwhile, the other experiments can't measure the CMB at lower values of $l$ around $l < 500$. I'm guessing that a ground-based approach with a large collector is required to get the high resolutions needed to measure the power of the component at high values of $l$. Is this correct?
What I don't understand is, why can't the other experiments get measurements in the lower part of the plot?