1 To make the logo more friendly
Google announced on their blog that they changed the logo to make it more colorful and friendly (See also how to use Neuroscience in web design).
2 To match the company's strategy
David Airey, author of Logo Design Love, said that the Serif typeface is more suited to traditional companies and that a company like Google needs a more contemporary logo (See also why do companies change their logos).
3 To help people who are afraid of technology
Some people suggested that the new change was done to encourage those who are scared of digital interfaces to feel more safe using Google.
4 To look better on mobile phones
Because the internet these days consists of so many different devices, companies sometimes have to change their logo to make it more visible on small devices (See also why Facebook Changed its logo).
5 To mirror Alphabet's logo
Some people suggest that this change was done so that Google's logo reflects the look of the logo of its new parent company Alphabet, which has a slick design.
6 To look simpler
Google said on its blog that one of the reasons the logo was changed was to make it look simpler (See why simple things are more likely to get popular).
7 To be able to easily transform the logo
Some people suggested that the new logo is easier for designers to manipulate because all the letters have one weight. This can enable Google to easily connect its different products together by giving them logos that share similar characteristics.
8 Too look uncluttered
Google said in their blog that the new design makes the logo look uncluttered.
9 To clearly associate the colors with the logo
Google has always been known for its color but as the logo became more colorful, according to Google, this can help the company's branding strategy (See why is branding so important for businesses).
10 To reflect the different Google services
According to Google's blog post 'It doesn’t simply tell you that you’re using Google, but also shows you how Google is working for you. For example, new elements like a colorful Google mic help you identify and interact with Google whether you’re talking, tapping or typing'.