Then why should we pay it any attention? We have a perfect explanation for the lumpiness we do see, an explanation that is not only very specific and detailed, but also accords with other observations. And that explanation precludes the possibility of a Milne cosmology. Unless you can present a model that has at least
as much predictive power as the current cosmology, nobody is going to care.
This isn't in any way the case. The big bang theory predicted the thermal spectrum. This was expected back when the CMB was first predicted.
And as for the lumpiness, at the time COBE was launched, there were two major competing theories that predicted its statistical properties: cosmic strings, and inflation. Inflation won out. This was apparent with COBE plus balloon data, but became blatantly and wildly obvious with WMAP.