How can they be offering such low fares in business and first cabins?

I am planning three trips from Sacramento to Europe this summer. Since they are holidays, I am a little flexible on my dates.

Flying from SMF, I try to book, if possible, via SFO/LAX and FRA/LHR to my destination. Upgradeable Y fares are running about $2000 to $2400 .... but using either SWUs or miles, few flights are available for upgrade.

So, I asked about premium cabins .... I can dream, right?

I was surprised that Z fares (even on the 747 new config UA 900-901 SFO-FRA-SFO) are around $2600 to $3000. Throw in $1000 and 80,000, I could upgrade to F.

But they also are offering a ton of A fares this summer. Roundtrip SMF-SFO-FRA and on to either HAM or Florence are only $5100 a.i. This is during June, July, and Sept.

Has UA always offered such low discount A and Z fares, or are these fares unusually low this year?