The universe is infinitely expanding in all directions, but since it's so old, it's had the opportunity to expand for quite a long time. With that in mind, the universe is huge, and it only continues to get mind-bogglingly bigger.
The vast size of the universe means light has to travel a long distance to get from point A to point B. Even though light is fast, it can still take a while to get from one side of the universe to the other given just how big it really is.
Nevertheless, we have space observation equipment that's almost powerful enough to see the edge of the universe, even if not directly. Our satellites are about to pick up activity produced by the Big Bang 13.8 billion years ago because the light had a long way to go in order to reach us, and it continues to do so.
None of our equipment can actually see the boundary of the universe in real time because the universe is expanding more quickly than the observable light can reach us. That's essentially why we can "almost" see the edge of the visible universe, and not effectively "see the edge of the visible universe."
