At most they have the indirect effect of using up silicon that might have been invested in performance enhancements. They also use up chip design time, but one would expect that cost to be repaid many times in applications development time savings. Developing a conviction that they are a good idea. Those of us who have developed programs on Multics or MCP are easily convinced, but those of us who haven't are in a majority. It is hard to sell a new architecture.
Life is more rewarding for people who do improved, compatible implementations of old ones.
There are obvious incentives to use available hardware, software, programming languages, network facilities, etc., even if atrociously malsuited to the application. A very thorough bounds test could be performed millions of times in the time that it has taken you to read this sentence. The test has done nothing to further the purposes of the program, but it has given you that much more cause to believe that the program is working properly. If something IS wrong, you know that you will know about it before it completely wrecks your program. They do nothing for the bridge, but they do help to guarantee that something infinitely more expensive than the bridge, namely a human being or his payroll record, won't fall into the waters below.