There could be several reasons why the uploaded quality may not be as high as the original video recording.
1) When videos are first submitted to the website, and you receive the link that you can go view it, you may only see the 720p version of that video. The reason is that it takes more time to process and finish uploading all resolutions. You should only have to wait a few minutes (depending on the length of the video) to see 1080 and any other resolutions.
2) You will want to ensure that 'Optimize videos for upload and share' is not enabled in the Preferences as that reduces the quality of the uploaded video. This option is mainly for those who wish to upload videos faster at the expense of reduced quality, or have limited bandwidth to upload videos. You can find this option in the Preferences under 'Advanced'