ER of MF vs ETF

Had a simple comparison b/w ER of MF vs ETF for some Vanguard funds.
It seems most of time ETF has lower ER than MF, except for Russell 2000.

Shouldn't ETF take more efforts to maintain?

MF ER ETF ER
Total VTSAX 0.04 VTI 0.03
SP500 VFIAX 0.04 VOO 0.03
Extended VEXAX 0.06 VXF 0.06
Russell 2000 VRTIX 0.08 VTWO 0.1
Dividend Appr VDADX 0.08 VIG 0.06

 

Could you tell what the abbreviated words are next time?

 

MF: Mutual Funds
ER: Expense Ratio