The R rating is a troublesome thing to deal with for the people who make movies. Whilst some genres; especially horror films; benefit from being rated R so they can deal with adult themes and include scenes that just wouldn't be appropriate for a younger audience, there's inevitably a financial impact. Locking some of the potential audience out means you don't get their money, and so box office success is harder to achieve.
It might have been tempting for Spielberg to edit the more violent and gory scenes out of this film to keep it away from an R rating and ensure as many people could see it as possible, but instead he chose to give us an accurate portrayal of the horrors of war. He was rewarded for it. 'Saving Private Ryan' was a #1 at the box office. It would take sixteen years before any other R rated film would achieve that position; 2014's 'American Sniper'.