The exclusion is usually accidental
Few municipalities intend to write a single-supplier tender. It happens through defensive drafting: a turnover threshold set high to reduce delivery risk, a reference requirement copied from the previous procedure, a single lot because splitting is administratively harder.
What the drafting costs
Fewer bidders, higher prices, and a market that learns not to bother reading the city’s notices.
The fixes are unglamorous
They are also cheap, legal under the existing framework, and available to any authority willing to redraft rather than reuse.