Why define dwarf galaxies as galaxies?

Namely, why we do not define them as star clusters or stellar associations?

The definition of a galaxy

1. The definition of a galxy from Kroupa et al. 20224:

Galaxy A gravitationally bound stellar population with a half-mass two-body relaxation time (i.e. energy equipartition time scale) longer than a Hubble time

2. From An introduction to dwarf galaxies

The relaxation time is the time after which encounters between stars can have changed their initial velocities (absolute value and direction) by order of itself. Galaxies can be considered as stellar systems where this cannot have happened within the age of the Universe.

Star clusters

A typical relaxation timescale of star clusters are of the order of ${10}^{7-10}$ years, which is much larger than a Hubble time. Please see lecture1 and lecture2 for more details.

Dwarf galaxies

Their relaxation timescale is shown in An introduction to dwarf galaxies