Factual error: Calendar date at the very beginning of the film (in the police station), shows the dates of Saturday 20th/Sunday 21st July 1983. However the 20th and 21st July 1983 fell on Wednesday and Thursday.
Factual error: At the very beginning of the film, Gunny Highway learns that he's being reassigned to the 2nd Marine Division. The 2nd Division, located at Camp Lejeune, North Carolina, is situated on the NC coast; there are no mountains in the immediate vicinity. However, when the Gunny trains his platoon, he does so in the hills of another Marine training camp located in California. There is a big difference between California and North Carolina.
Factual error: Towards the end of the movie Lieutenant Ring is ordered to escort the rescued students to Cherry Point. When they arrive they are actually at MCAS El Toro, not MCAS Cherry Point. Any Marine who has been at both air stations can immediately tell the difference.
Factual error: At the end of the movie when Gunny Highway and his men land at what is supposed to be Cherry Point, the band playing the music should be the 2nd Marine Aircraft Wing Band, but is in fact the 1st Marine Division band as can be seen by the 1st Marine Division insignia on the drummer's drum.
Factual error: When the Recon Team were in Grenada, you don't see Swede carrying extra ammo belts for his M60. Neither does he have a buddy who could carry the additional combat load assuming they would be in boxes.
Factual error: When Highway is walking in front of the flag pole, the colors are being retired and the bugle call is "Taps". When the colors are retired the bugle call is "Retreat". Taps isn't played until lights out at 2200 hours (10 P.M.).
Factual error: As they are walking among some trees in Grenada, during an overhead shot an American robin's warning call is heard. There is no way that bird is on Grenada.
Factual error: During training and the invasion of Grenada scenes they show the Marines wearing PASGT Kevelar helmets. Marines did not wear PASGT helmets until 1984. The invasion of Grenada was in 1983.
Factual error: If Highway has been in the Marine Corps for 24 years, as Major Devin pointed out at the 9:45 mark, that would put Highway's entering the Marines at approximately 1959 (the beginning of the movie shows July 1983 as a timeline reference). But the Battle of Heartbreak Ridge took place in Sept-Oct of 1951. Moreover, Sargent Major Choozhoo was regaling "Stitch" Jones about the exploits in Vietnam that earned Highway the Congressional Medal of Honor. Two separate wars. (00:09:45 - 01:19:50)
Answer: It's because it's a movie. The plot could not ably handle the stories of twenty different characters while maintaining the action's pace and a cohesive story line within a two-hour time frame. It instead focuses on a few key characters.