It is up to those sites to weigh those competing considerations and determine what is worthwhile for them. There may be valid reasons for taking a looser stance on moderations -- you have articulated several of them -- but there are also valid reasons for moderating content more strictly. More traffic isn't necessarily the only goal; it may also be important to retain experts and answerers, maintain quality standards, and/or support the community. One of the great things about the Stack Exchange network is that we empower individual sites to consider all these factors and establish their own standards, based on their community's needs.
If by asking here you are seeking some network-wide policy or guidance that would push small sites to change their moderation practices, I would advocate for a different approach. Instead, I would suggest first understanding possible reasons why that site might have chosen a narrower scope; then if you still think a change in scope is warranted, post on that site's meta and see whether your arguments gain support from that site's community. If you approach it with an attitude of understanding and respecting their community's norms and expectations before trying to change them, that may go a long way.