The question refers to the concept known as the "missing satellite problem" or "missing dwarf galaxy problem". According to the predictions of cosmological simulations based on the prevailing Lambda-Cold Dark Matter (ΛCDM) model of cosmology, galaxies like the Milky Way should have a much larger number of small satellite galaxies in their vicinity. However, observations show that the number of observed satellites is much lower than expected.

The reasons behind this discrepancy are not yet fully understood, but there are several possible explanations:

1. Baryon effects: Baryonic processes such as supernova explosions and the buildup of gas in galaxies can expel gas from the galaxies, preventing some satellite galaxies from forming or stripping them of their gas, making them less visible.

2. Modified gravity: Some alternative theories of gravity propose different models for how gravity works on large scales, which can affect the formation and dynamics of galaxies and can lead to a lower abundance of satellite galaxies.

3. Photoionization and reionization: During the early universe, the intense radiation from early stars and quasars could have ionized the intergalactic medium, making it difficult for small satellite galaxies to form.

4. Angular momentum problem: The ΛCDM model predicts that satellite galaxies should have high angular momenta, but observations show that many satellites have low angular momenta. This discrepancy could affect their ability to form and survive in the presence of the Milky Way's gravitational influence.

Solving the missing satellite problem is an active area of research in astrophysics, and further observations and theoretical studies are needed to fully understand the reasons for the discrepancy between observations and predictions from simulations based on the ΛCDM model.