Why doesn't the GOOGLEFINANCE function work inside a calculated field in a pivot table?

I can use VLOOKUP to find something from a calculated field, but the GOOGLEFINANCE function just gets stuck loading forever:

In this example, GOOGLEFINANCE is used to find the stock name, the "Tag" column is a VLOOKUP

Here's the config for the calculated fields:

Sample spreadsheet:

https://docs.google.com/spreadsheets/d/1AtHqomrfOt5x_vxGuMby88kg51sNhJn92LMl3EAjU5A/edit?usp=sharing

I know I could move the GOOGLEFINANCE call out of the calculated field, but I'm interested to know why it doesn't work in the calc field.