Why is the angle between the C-H bonds in the methane molecule equal to 109.5

Why is the angle between the C-H bonds in the methane molecule equal to 109.5, and in the ammonia molecule the angle H-N-H is 107?

CH4: Orbitals involved in hybridization – s, p, p, p. The type of sp3 hybridization is hybridization. The spatial form of the molecule is tetrahedral. The angle between the bonds is 109.5.

NH3: Orbitals involved in hybridization – s, p, p, p. The type of sp3 hybridization is hybridization. The N atom is in the sp3-hybrid state. Of the 4 hybrid nitrogen orbitals, 3 participate in the formation of single N – H bonds, and 1 sp3 – the hybrid orbital is occupied by a lone electron pair. It can create a donor-acceptor bond with H +, forming NH4 +, and is also the reason for the deviation from the tetrahedral angle in the structure to a value of 107.