My guess is it has something to do with the formatting of the receipts. ibotta likely has an expected format for each store so they know how to interpret it. The pickup and delivery receipts that look different than the regular checkout ones from the store are probably not able to be handled.
If they don't currently take them, it could take months or even years to do necessary coding changes to allow this. depending on a multitude of factors.
I personally don't do curbside or delivery. I disinfect before I enter store. I touch whatever I choose in store, I make sure I don't touch my face, and when I am leaving. I sanitize again before I get in the car. That may not be perfect, but I trust me better than I do everyone else. I personally worry more about touching things than people sneezing on me. And I have no idea what 'pickers' are touching when selecting my items, and I don't know for sure they are wearing a mask, so it is just an extra person I need to worry about. At the end of the day you are touching all the things they touched when picking your order.
Your account needs to be linked to ibotta. walmart target pickup no receipts you need to link. Any other store you need to read them some have a link only option but are not for pick up they're in store only. Also is you go on the app click on the grocery pick up option all the stores that allow pick up will show then you can click on the store and link your account.