[closed] Why do companies stay current instead of sticking with what works?

In you question you mention: "There is a saying to not mess with things that are not broke, thus if it aint' broke, do not fix it. However, I notice that different companies sometimes modernize their packaging and logo designs". There are many examples of companies changing to "stay current" and many examples of companies "sticking with what works" and not changing. Business practices and strategy are very different from branding decisions (although branding is part of strategy). I will attempt to respond to some of your question but my response will in no way be complete.

1. Logos & Branding
Starting with branding since it directly responds to your question: Logos and (to some extent) packaging get to some of the core pieces of branding. Logos are the face of the company and should quickly communicate what the customers should know about the company. Coca Cola has a very recognizable brand despite its globally diverse market. Simply seeing parts of the logo (i.e. the red, the swoosh, or the letters) makes people think of Coke. Pepsi, on the other hand, recently, successfully changed their logo. The decision to stay the same or change may be driven by value and effectiveness of the brand and also the target customer segments. Pepsi's target segment [in the U.S.] tends to be younger drinkers (it's even a sweeter drink than coke). Since the primary target is younger they are more likely to accept a significant shift in the logo. Gap, on the other hand, recently tried to change their logo and the customers revolted so much that Gap quickly reverted.

There are other reasons to change logos too. For example, google recently made subtle changes to their logo. The new Google logo now requires less data so their page loads faster. Specifically to your question on Walmart, naturally they have their reasons for changing their logo (I believe the corporate story is that the most recent change was to reflect the "refresh happening in their stores". the fact you are seeing different versions of the Walmart logo (the old with the Star-hyphen vs. the new with the star at the end) probably has more to do with the fact that it is very expensive to re-brand all of their assets and the life of truck trailers is quite long; however their shipping boxes without a doubt their boxes and in-store logos are all the new ones. In summary, there are lots of reasons change or don't change their logo. There is no one rule of thumb for success it depends on the target market, the message the company wants to communicate and the customers' response to the brand.

2. Packaging
Packaging is a combination of form and function. First function, the packaging must enable you to get your product undamaged to your customers' homes. For example if eggs were sold in bags instead of egg cartons they would break before they got to the store. Companies will also design packaging to ensure efficient shipping (i.e. egg cartons protect eggs, but you can also stack them and easily ship them).The more product you can get on a truck then the lower the shipping costs which means I can earn more profit and/or lower my price. As a result, some companies may change their packaging to more efficiently deliver and protect their product. This is also why a lot of packages are rectangular.

If you are talking about design on the packaging, that ties back to logos and branding. It is dictated by what the company is trying to communicate to its target.

3. Strategy and Business Activities
You question asks why companies try to stay current rather than sticking with what works. From a larger business sense this is a much more nuanced answer. There are many companies that are likely to keep doing what they've been doing without considering if it is the best way to do things or if the customers are remaining loyal or needful of the product. This could be a reflection of the industry (i.e. low levels of competition). It could also be a reflection of the complexity within a company (i.e. its hard to upgrade systems or get the political support necessary to change).

On the other hand there are other companies that are constantly changing trying to leading edge of opportunity.Some of these companies have been significant disruptors in their industries (look at Intel when they switched from memory chips to processing and came to dominate the industry). Facebook is an example of a company that quickly evolved to overcome most (and maybe all) of the networking websites. There are also examples of companies that keep trying to change but never seem to find their stride or lose their economies of scale. Change for the sake of change without strategy or good execution can be disastrous for a company. For example, when JC Penny tried every day low pricing and got rid of their sales it almost destroyed the company. it was a great idea, but it didn't work with for the customer segment.