"Copyright" depends greatly on where a company is based and laws in any particular region. Whether or not something can be copyrighted depends greatly upon where the copyright is being filed. In the US, generally you can copyright how something is presented or displayed. However, simply because something is copyrighted in the US, that does not mean any other country has the same copyright laws and will honor the US copyright. In terms of a web site, typically it's specific visual aspects and content which is copyrighted and not the "web site" as a whole.
I do not know specifically, but it's possible that Facebook, Apple et. al. has copyrighted the specific appearance of their chat bubbles.
You can trademark what is referred to as "trade dress". This is the basic appearance of a brand as seen by the public and can include colors and general descriptions of visual elements. This is done to prevent a company from "piggybacking" on another company's success.
To use an example, UPS has trademarked their brown color for trucks, uniforms, and other items. So, a new package delivery service, let's call it DeliveryX, can't use brown trucks and brown uniformed drivers to deliver things. If DeliveryX does use brown trucks and uniforms, they are specifically confusing consumers as to who they are and using the brand recognition of UPS to imply their own brand is the same or similar. They are essentially "stealing trust" from the consumer.
Be aware trademarks are not the same as a copyrights. Trademarks don't give ownership over anything, where as copyrights do. Trademarks simply serve as a notice to other business that "we use this, don't try and use it yourself". Lawsuits can derive from trademark disputes. Apple has taken Samsung to court countless times (and vice versa) for what Apple feels is a violation of their trade dress trademarks - as in "look and feel" of Apple's products.
To this end... if a filmmaker wishes to avoid any such issues, the simplest thing to do is create your own. That way there's no chance someone is going to get the idea you are trying to "piggyback" on their trade dress.
When you look at things like a UI or chat bubbles, their appearance is generally specific to a given platform. Therefor if a film maker used the bubbles from any platform, there's the possibility the platform could complain. When you consider these platform are multi-billion dollar companies with massive legal teams, who would want to run that risk? So.. they create their own.
Another possibility is visual continuity. Some films just look worse if you use big blue and green bubbles on screen or something similar. So they may have created their own just to maintain the visual continuity of the filmed piece.