"Because the index needs accuracy.", and I would argue that include price accuracy not just inclusion accuracy. The S&P is a benchmark that is designed to reflect a subset of the market, and giving only some companies early access to the benchmark changes the benchmark. So if you want a benchmark that's designed to include all the big stocks regardless of age, profitability, etc then go make a new benchmark. The only thing you need to do is convince others to use your benchmark.

"go make a new benchmark" completely ignores how this works in practice. Benchmarks are only useful because everyone uses the same one, you can't swap it out. The S&P 500 benchmark is used as a comparison for trillions of dollars of mutual funds, index funds, and institutional mandates. The further the S&P 500 strays from reflecting the actual market, the more useless it becomes.

Also the S&P criteria have been revised multiple times, it's not some sacred unchangeable document.