This may happen to be true for some businesses, but it's not necessarily true. Some toolsets may make it hard, which raises the I. Others make it easy or free, so people naturally do it. The smaller the I gets, the more likely a given R is worth it.

I also think it's easy to underestimate the R here. It's very hard to detect things like brand damage and lost leads, especially when somebody turns up on your site once, thinks you guys are chumps because of a bad first impression, and never comes back. Whereas the I is obvious, because the cost is all internal to the company.

The two factors, alas, reinforce one another. Link rot isn't an obvious problem when setting up a system, because nobody is linking in. By the time the problem becomes noticeable, the system is hard to change, making the cost of a fix high. And that trains people to treat link rot as unimportant, deepening the cycle.