One reason is it sets a precedent that the executive branch can make up whatever rule they want.
If they want to force everyone into house arrest then make the legislature write a law.
If they want to mandate the masks then make the legislature write a law.
The governor is abusing the authority given under emergency action and applying blanket laws to enforce whatever "public health" justification he wants.
At some point is it no longer an emergency and he can't keep issuing executive orders as he wishes in place of laws.
Oh, but isn't it convenient that in 2018 the legislature passed a law that made several modifications to the revised statues.
https://leg.colorado.gov/bills/hb18-1394
The changes came to Title 24, Article 33.5, Part 7 - Emergency Management - that now gives the governor the decision on when an emergency is no longer an emergency without any time limits other than every 30 days he has to renew the declaration.
https://codes.findlaw.com/co/title-24-government-state/
It's curious too that Parts 704.5 and 711.5 were added with many detailed powers specific to an epidemic response. The only other type of emergency that has its own part is 711 dealing with compensation for grasshopper infestations.
Do you suppose now that he's got the power he'll ever want to give it up? What do you think the chances are this infection never goes away or only goes away when the governor is satisfied we've jumped through enough hoops?
What's the point of pushing back? The governor has already decided what jobs and medical treatments he deems worthy of continuing. That choosing when and where you want to go is a public health issue.
So what's to stop the governor unilaterally deciding gasoline engines are a public health issue for lung recovery?
That deep lugged tires churning up dust off highway is a public health issue from the particulates?
Cigars are a public health issue?
The legislature knows political hot buttons (see the OHV fund raid and the effectiveness of public pressure) and that it would be difficult or perhaps even impossible to legislate much of this into effect with an immediate reaction and probably losing re-elections. But they are with him on principles since they can reign it in anytime they want.
And what's the governor care? He's not up for re-election until 2023 and is worth it would seem around $350 million. It's not easy to unravel his companies (last reported finances were 2017 when in Congress) but appears between the various Jovian and Mountain Property Improvement companies his primary residence may sit within roughly 60 acres over in Weld County. So even if there is an election in 2023 and he happens to lose he'll be just fine.