testnet – Why is the source code fee calculated higher than the current bitcoin fee amount?

In python bit (https://github.com/ofek/bit/), when sending a message, it is properly 80 bytes or less (https://developer.bitcoin.org/devguide/transactions.html) fee is If it is a 4-byte character string, it is about 0.03 $ / 140 = 21428 satoshi (https://mempool.space/ja/testnet), but it is often 80,000 or more.
Why is the source_code fee calculation result always higher than the actual testnet?

I thought about the cause as follows.
1: There is a possibility that the calculation method of source_code is wrong. (Target + min_change + estimated_fee is the calculation method of fee, but I don’t understand why the limit(default 80) is multiplied in the next code part. )

output_size = (len(address_to_scriptpubkey(o(0))) + 9 for o in outputs)
    output_size.append(len(messages) * (MESSAGE_LIMIT + 9))
    output_size.append(len(address_to_scriptpubkey(leftover)) + 9)
    sum_outputs = sum(out(1) for out in outputs)
  (by transaction.py) ```

How can I send a transaction to testnet with the fee properly set below 80000?