They’re horizontal stabilizers. They serve a crucial aerodynamic role.

https://en.wikipedia.org/wiki/1983_Negev_mid-air_collision

In May 1983, two Israeli Air Force aircraft, an F-15 Eagle and an A-4 Skyhawk, collided in mid-air during a training exercise over the Negev region, in Israel. Notably, the F-15 (with a crew of two) managed to land safely at a nearby airbase, despite having its right wing almost completely sheared off in the collision. The lifting body properties of the F-15, together with its overabundant engine thrust, allowed the pilot to achieve this unique feat.[1]

The F-15 started rolling uncontrollably after the collision and the instructor ordered an ejection. Nedivi, who outranked the instructor, decided not to eject and attempted recovery by engaging the afterburner, and eventually regained control of the aircraft. He was able to maintain control because of the lift generated by the large areas of the fuselage, stabilators, and remaining wing. Diverting to Ramon Airbase,[2] the F-15 landed at twice the normal speed to maintain the necessary lift, and its tailhook was torn off completely during the landing. Nedivi managed to bring his F-15 to a complete stop approximately 20 ft (6 m) from the end of the runway. He later told The History Channel, “it’s highly likely that if I had seen it clearly I would have ejected, because it was obvious you couldn’t really fly an airplane like that.”[4] He added, “Only when McDonnell Douglas later went to analyze it, they said, OK, the F-15 has a very wide [lifting] body; you fly fast enough and you’re like a rocket. You don’t need wings.”[3][4][5]

Sometimes things aren’t as crucial as they might seem!

Crucial, but depending on the design technically not required! There are designs of planes where the entire plane is just one big wing. Buuuuuuut having the traditional rudder, aileron, and elevator is tried trued and reliable.