Why was the house vote closer in Colorado?

[VAR]

Yes, Democrats underperformed in the suburbs, which is basically what happened nationwide. For example, Trump won El Paso County (Colorado Springs) by 11%, Gardner won it by 16%, and Doug Lamborn (the Republican incumbent in CO-05) won it by 19%. Likewise, Jason Crow did two points worse than Biden in CO-06 (Denver suburbs). Biden, Hickenlooper, and Mitsch Bush all won Pueblo County, yet the latter two did a tad worse than the former.

Here's the results by congressional district:

CO-01 (City of Denver): Biden +53.5, DeGette +50
CO-02 (Boulder + Fort Collins): Biden +30, Neguse +26
CO-03: (Western Slope + Grand Junction + Pueblo + ski towns like Aspen): Trump +5.5, Boebert +6
CO-04 (Eastern Plains): Trump +16, Buck +23.5
CO-05 (Colorado Springs): Trump +13, Lamborn +20
CO-06 (Aurora): Biden +19, Crow +17
CO-07 (West Denver suburbs): Biden +23, Perlmutter +21.5

https://www.dailykos.com/stories/2020/11/19/1163009/-Daily-Kos-Elections-presidential-results-by-congressional-district-for-2020-2016-and-2012

It's worth noting that it's not just suburban ancestrally R Biden voters splitting their tickets, though. Ken Buck performed significantly better than Trump in his rural district.

[VAR]

Yes, Democrats underperformed in the suburbs, which is basically what happened nationwide. For example, Trump won El Paso County (Colorado Springs) by 11%, Gardner won it by 16%, and Doug Lamborn (the Republican incumbent in CO-05) won it by 19%. Likewise, Jason Crow did two points worse than Biden in CO-06 (Denver suburbs). Biden, Hickenlooper, and Mitsch Bush all won Pueblo County, yet the latter two did a tad worse than the former.

Here's the results by congressional district:

CO-01 (City of Denver): Biden +53.5, DeGette +50
CO-02 (Boulder + Fort Collins): Biden +30, Neguse +26
CO-03: (Western Slope + Grand Junction + Pueblo + ski towns like Aspen): Trump +5.5, Boebert +6
CO-04 (Eastern Plains): Trump +16, Buck +23.5
CO-05 (Colorado Springs): Trump +13, Lamborn +20
CO-06 (Aurora): Biden +19, Crow +17
CO-07 (West Denver suburbs): Biden +23, Perlmutter +21.5

https://www.dailykos.com/stories/2020/11/19/1163009/-Daily-Kos-Elections-presidential-results-by-congressional-district-for-2020-2016-and-2012

It's worth noting that it's not just suburban ancestrally R Biden voters splitting their tickets, though. Ken Buck performed significantly better than Trump in his rural district.

Ken Bucks district is not really rural. 80% of the district lives in Douglas or Weld.

Yes, it seems that you're right (I'm surprised, given its size).

[VAR]

I can get a Biden-generic R voter, but who would split their ticket for Boebert! It really concerns me that people like Boebert and MTG overperformed Trump in their districts.

Honestly, from an objective standpoint, Lauren Boebert is a Generic R.