I can see why cosplayers/photographers want to seek their permission first before it gets uploaded as they may want to make sure that credit to those involved are there and correct. I also understand it seen as potential likes/traffic being taken away from the cosplayer, reducing of further work of theirs not been seen. I can understand knowing where there photo will end up, so they can see what content the blog has.
I know there are many cosplay blogs on facebook, twitter, tumblr and Instagram who just copy/take the images from there page or where ever they find on the internet and just upload, with either a generic post, plain text of the person with no tagging. I've even seen posts where they share the photo but you can see the post is mainly promoting their own material on their website.
I feel, if you have uploaded a photo onto the public domain such as facebook or instagram, then you run the risk of people taking your work and using it onto their social media platform. If you don't want your work used like this, then I would suggest to create a giant watermark saying "DO NOT USE" across the photo or don't upload your the photo, cause the bloggers like myself, rely on the openness of the photos being to reshare onto their platform.
BUT, for all of that, I am thankful to all bloggers out there who are using my photos and crediting me correctly. This is just my opinion on this matter, but the reason why I am thankful for bloggers who use my photos on their blog and credit me, I'm reaching to a wider audience which previously I've never used to. Also, it's humbling to know, someone thought it was worthily enough to share onto their blog, main times I have sent my work into magazines, online publications and they have not replied back.
I just want to mention one blog whom I have the most respect for what he does and that is Titans of Cosplay. This blog and there other franchise specific blogs, always make a point making sure to credit everyone involved. In fact he is the main reason I am also a blogger of cosplay and run things similar to how he does. He has spend as much free time as I do setting up and queuing up photos he comes across the network of pages. I am grateful the number of time he has used my work on his feed.
I really appreciate people who want to have a greater control of their photo online, but I really think if you require permission for photos to be used on there site, you best stop uploading photos. Those who are limiting usage of their photos on blog, reduce the exposure of their work to a greater audience.