You're only seeing the final product, not the work that goes into it. You might have graphics designers churn out a dozen or more different variations. Those logos need to be checked against any other existing trademarks. At some point, they also need to be tested in focus groups so that the average person can draw a link between the old logo and the new one; or if it's a new logo completely, ask if the logo makes enough of an impression for people to remember it later. There's research into whether the logo can be recognizable in all kinds of situations (e.g., what happens if you shrink it down to a 32x32 pixel square for social media? Etc.). Then there's all the regulatory and business hurdles of actually updating it.