A normal baryon, such as a proton or a neutron, is composed of three quarks held together by the strong nuclear force. According to the principles of quantum chromodynamics (QCD), which describes the interactions of quarks and gluons, the combination of quarks within a baryon must satisfy certain rules and constraints.
One important rule is that the total color charge of a composite particle must be colorless or "white." Quarks come in three colors: red, green, and blue, and antiquarks come in three anticolors: antired, antigreen, and antiblue. In a baryon, the three quarks combine in a way that results in a net color charge of white.
The top quark is the heaviest of all known quarks and has a charge of +2/3 (in units of the elementary charge). The combination of three top quarks would result in a net color charge of 2/3 + 2/3 + 2/3 = 2, which violates the requirement for a colorless state. Baryons are always color-neutral, so they must be composed of quarks with different colors. This is why a normal baryon cannot be made up of three top quarks alone.
Furthermore, the top quark is extremely short-lived and decays very quickly into other particles, primarily a W boson and a bottom quark. Its short lifetime, combined with its large mass, makes it difficult for top quarks to form stable bound states within a baryon. The typical hadrons (particles composed of quarks) involving the top quark are mesons, which consist of a top quark and an antiquark.