Explain why some tokens might not have FIAT value

CS team reported:

FIAT VALUES FOR TOKENS MISSING we get tons of tickets about this, and it's pretty hard to capture an automated reply for them via keyword so it becomes quite a time-suck for support. Can we review how we are pulling fiat values (currently I’m told it is based on an eth-conversion, and therefore low-value tokens won’t convert) in order to get people the values for their tokens

Cross-product
Some tokens do not have Fiat value, and users are surprised by it

Start by tracing how the app currently obtains fiat values and where the reported ETH-conversion behavior is handled. The issue does not name files or tests; completion would require explaining missing values to users and determining whether low-value tokens can receive fiat values.

Written by the indexing model from the issue text.