Probably the size, those are pretty huge to insert as attachments (6240 x 4160 pixels @ 2.7MB and 3.5MB). The other is 4295 x 2864 (2.1 MB). I tried manually editing the code in your post and couldn't get them to display either.
Unless there's a good reason to post an attachment that large (because the detail is important when you zoom in, for example) I would advise against it. I believe the forum software will automatically shrink any image larger than ~800 pixels wide.
Very pretty shots though!