Why do hot objects prefer to emit photons over electrons ? Is there electron-positron annihilation ? If so , why ? Im confused by this.
The energy levels in any object are quantized. The ground state of an electron is the lowest energy. From there electrons can have many higher energy levels, the highest being that which allows them to complete escape the nuclear attraction, i.e., get emitted.
So hot objects can emit electrons but the probability that any single electron will have that much energy just due to heating the objected is lower than electrons going up a few levels (due to gaining thermal energy) and then jumping back and emitting photons. Very hot objects can become plasma (electrons are emitted and you are left with ions). There are of course other ways to achieve a plasma (e.g., die-electric breakdown discharge) which are not equilibrium thermal excitation. But that is beyond scope of this question.
Electrons are emitted, but being charged, they form a cloud close to the surface and do not travel too far due to attraction to the positively charged remainder. If you place a metallic plate near the surface, you can collect these electrons and even make a circuit. This is known as thermo-electric sources of electricity.
Photons are neutral and are not attracted to the hot body, so they go away.
Edit: There are no positrons there, but positively charged atomic ions. In a hot object there are processes of atom excitation/ionization and recombination. The latter process produces photons.