I understand why this exists for regular sites – a negative score indicates that there is something wrong with the question, and if the question retains its negative score for that long, then it might not be worth keeping on the site. However, on meta sites, a negative score – particularly when it comes to feature-requests – is merely indicative of disagreement. A question can have a very negative score without there being anything wrong quality- or research-wise with the question. It might merely be a suggestion that more people disagree with than agree with. Currently, even if the disagreers only have one more member than the agreers, the question will still be automatically deleted.
This does not seem like a good system. Questions that are otherwise fine may be getting deleted just because one or more people disagreed with the suggestion than agreed with it. In fact, I just noticed a case where this happened. This question has 10 upvotes and 25 downvotes for a total score of -15, and was therefore automatically deleted under the policy of RemoveDeadQuestions. However, there doesn't appear to be anything wrong with the quality of the question (full disclosure: it's my question); it's just that more people disagreed with it than agreed with it. By deleting this post, the record of the discussion is lost (except to those who have 10,000 reputation).
As the record of the prior discussion is lost, it also means that users who later come up with the same idea will not be aware of the prior discussion, or the fact that it had been proposed before and received negatively, and may sometimes be hit with an immediate onslaught of downvotes simply because they didn't know of the prior outcome. Also, such questions cannot be closed as duplicates, impeding content curation - users will have to repeatedly explain the reasons why the request is not a good idea.
I think it would make sense to not apply the policy of RemoveDeadQuestions to Meta questions. Or, at the very least, the criteria should be tweaked. Perhaps if a question has a negative score and no upvotes it should be deleted, as there it is more likely that the negative score is because it's a bad-quality question. But when the question has a significant amount of upvotes it should not get deleted simply because one more person voted against the suggestion than in favor of it.
Some may argue that since nobody bothered to answer the question (which stops it from automatic deletion), the discussion isn't valuable, but in many cases, there may be a valuable discussion in the comments, and as Monica's answer states, feature requests are expected to make their case in the question, not in answers. Even if the author or someone else edits the question to have better arguments, the question would still be automatically deleted if it doesn't accrue enough upvotes to counter the downvotes.
(I am aware of this question which asks if RemoveDeadQuestions applies to Meta. The point of this question is to suggest that that should not be the case.)