I was racking my head trying to figure out why I loved Marathon's artstyle so much and finally figured it out when I saw a tweet (final collage is from said tweet) from Marathon's own Franchise Art Director at Bungie, Joseph Cross.
They're calling back to the y2k era of TDR and WipEout. I ADORE the WipEout series and the artstyle from that time period had a profound impact on me growing up and seeing this style being iterated on 25 years later is so refreshing and exciting.