Not all investment is for a capital gain over time.
Some is for income. Stocks that pay a good dividend provide good income, but in states with income taxes that is taxable income. Bonds pay income, but in most states federal treasury bond income is not taxable, to the state. That makes some bond investments a good deal where some income, not just capital gains, is whate someone is looking for.
And that is the best argument in support of bonds.
A stable income in stable times, not something to be laughed at or scorned.
One size never fits all, and that's why I enjoy hearing how other people approach money matters.