Many commentators refer to a player's 40-yard dash time to make a point of how fast a player is. This is admittedly relevant by the time of the draft but not so much afterwards, one would think. Many fast receivers can't make it to Combine due to injuries every year, and it doesn't mean that they are any slower than others. Similarly, just because a player has had a relatively good/bad time once doesn't mean that they will perform at that level consistently throughout their career. There is a thing called a decline, and another thing called improvement :)
Considering the amount of technology that is available, one would think it would surely be possible to get more up-to-date measurements of running speed and/or acceleration. Why is the combine 40-time still a thing after years in the NFL?