Twitter's morphing into a media company, or at least that seems to be the goal. As such, it needs to get its content, which in its case is someone else's creations, distributed as widely as possible.
Embedded tweets are a great tool for that. The feature was introduced a few years back to make it easier for people to quote tweets while still retaining context and links to the original tweet, the profile and so on.
Now, Twitter is doing another big change to the embeddable tweets, adding more context and features, i.e. photos, videos and whatever else people attach to their tweets.
"Embedded Tweets display photos, videos, article summaries and other content shared in a Tweet, just like you see on twitter.com," Twitter explained
"You can also view retweet and favorite counts to better understand engagement, and we’ve made some tweaks to the design so that embedded Tweets are easier to read," it added.
Twitter also boasts that embedded tweets will load faster than before, though that's probably going to be offset by having to load more stuff if there's a video or photo attached.