Same reason the Russians sent their state of the art aircraft to North Korea and North Vietnam. Using Russian provided gear, North Vietnam shot down 10,000 US aircraft.
https://en.m.wikipedia.org/wiki/List_of_aircraft_losses_of_the_Vietnam_War
https://en.m.wikipedia.org/wiki/List_of_aircraft_losses_of_the_Vietnam_War"
What a load of crap. North Vietnam did NOT "shot down 10,000 US aircraft." What's your agenda?
From that same link:
"In total, the United States military lost in Vietnam almost 10,000 aircraft, helicopters and UAVs (3,744 planes,[3] 5,607 helicopters[2] and 578 UAVs[1] )."
"Lost," as in, total losses from combat, from accidents, etc. Also includes UAV's. One example: Navy - SH-2/UH-2 Sea Sprite—12 lost, 0 in combat. Those 12 "lost" are part of the "total" and yet zero of them where "shot down" by the North Vietnamese and their Russian "gear."
"United States Air Force
All told, the U.S. Air Force flew 5.25 million sorties over South Vietnam, North Vietnam, northern and southern Laos, and Cambodia, losing 2,251 aircraft: 1,737 to hostile action, and 514 in accidents. 2,197 of the losses were fixed-wing, and the remainder rotary-wing. The USAF sustained approximately 0.4 losses per 1,000 sorties during the conflict, which compared favorably with a 2.0 rate in Korea and a 9.7 figure during World War II.[9][10]: 268 "
At 0.4 losses per 1,000 sorties, the USAF kicked commie Azz in Vietnam.
"United States Navy
Twenty-one aircraft carriers conducted 86 war cruises and operated 9,178 total days [edit: or 25 years per their numbers] on the line in the Gulf of Tonkin. 532 aircraft were lost in combat and 329 more to operational causes, resulting in the deaths of 401 naval aviators, with 64 airmen reported missing and 179 taken prisoner of war."
So, in over 25 years, the Navy lost 532 aircraft (of all kinds) to combat, or roughly 1 aircraft every 2 & 1/2 weeks. The USN also kicked commie Azz in Vietnam.
"United States Marine Corps
U.S. Marine Corps aircraft lost in combat included 193 fixed-wing and 270 rotary-wing aircraft."
Considering the Marines' mission and operating environment in Vietnam, loosing 463 total aircraft throughout the entire war, I'd say is also kicking commie Azz.
As far as actual Air to Air combat...the U.S. "gear" made fools of the Russian "gear"
Even the lowest 3.8 to 1 ratio is a significant enought advantage.