Anybody else notice that it seems the difference in fare price between Basic Economy and Main Cabin has gone up in the past few days?

Was asked for $35 each direction to upgrade to main cabin fare from DEN-MIA (via MSP), and $25 each direction for DEN-CSG (via ATL), never have been asked for more than $15/way before on a standard route connection under 4 hours from DEN-AAA-BBB...

Seems to me DL is following UA in increasing these fare differences to me, as UA went from $15 on most of my DEN routes to $40... from me

Hopefully just unlucky on my part, but I'm not too hopeful