Continual growth might actually make it more difficult because it raises our infrastructure costs and we need to update our database and other functionality to deal with the growth. This is not to say we don’t want more people to use iNat - we do! - but as iNaturalist doesn’t charge fees for use, nor do we sell our users’ personal information, I want to be clear that growth in use is not necessarily coupled with growth in income.
Adding the infrastructure to upload, play, and store video files, plus the user interface and design work for it, is a pretty heavy lift, and as mentioned above it’s something we want to do (I voted for this request) but we’re limited by resources, or lack thereof. In the meantime, there are workarounds involving other sites like Vimeo, YouTube, Google Photos, DropBox, etc, where you can upload videos for free and link to those in your observation (eg this observation of mine).