TLDR: yeah, apologies, we know, we are working on it, it will take time.
Long version. This is as expected. While we are trying to move to https first, at the moment we only support http. The reason is a bit complex.
Our URL naming structure for meta sites sucks for https, as every meta site at the moment would need a specially crafted certificate. This is hugely expensive in terms of ongoing maintenance. Main sites are fine because we have a cert for
*.stackexchange.com which we can reuse. Before the end of the year we want to migrate all metas from
<site>.meta.stackexchange.com, this allows us to purchase a
*.meta.stackexchange.com certificate and cover all of them.
The problem is that we need to migrate all references to the old metas first to the new metas (and to https). And this is a bunch of work, think of posts, comments, help pages... etc.
Furthermore, we need to migrate all the linked resources to https: images, avatars. Again -- a lot of work, which is also dependent on whether we can guarantee a http version or not. Gravatar needs to support it, imgur needs to support it, etc. etc.