Why does ChatGPT (CustomGPT) can't edit Google Sheets?

Hi everyone!
I would like to get your opinion/feedback/ideas why does OpenAI (I see Gemini as-well) struggles to integrate with Google Sheets.

The main issue I am facing is that everytime I ask ChatGPT to write something to Google Sheets (which has been connected thorough their UI) it fails to do that and just gives me an .xlsx file with changes. It’s kinda annoying to be able to just pull the data but not being able to change it.

On the other side I unfortunately wasn’t successful with CustomGPT (in connection with Google Sheets API) either, mainly due to weird access issues. I tried both with API key and OAuth but in both cases it didn’t worked well in long term.

For now I have resolved this by using Python,Responses API and Google Sheets API.

So the main question: Have you faced similar issues as-well ? If yes any ideas why it doesn’t integrates good?