Why do I get constant DC 2.5V when level shifting +/- 5V to 0-3.3V (LM741 op amp)?
The datasheet for the LM741 shows the power connections to be different from your circuit.

Here's the pinout for the LM741:



Pin 8 is "NC" which stands for "not connected."  Pin 7 is the proper V+.

Asside from that,  you can't run a 741 from 3.3V.

Its inputs and outputs must all stay a couple of volts away from the power rails.  That's more than your supply voltage, so you can't expect the 741 to do anything useful.