The cost of running 28 servers is not negligible compared to developer time. If a server goes for, say, $150 per month that's $4200 wasted each month. And contrary to the rewrite, the server cost is perpetual, so the rewrite amortises eventually.

Obviously, the economics of a rewrite depend very much on the size and complexity of the code base, but it didn't sound like they had a huge code base at the time of the rewrite.