Speakers + Amps = Powered Monitors
Powered monitors make sense for a lot of reasons. Except for very small models they are generally bi-amped, with an active line level crossover filter dividing the high & low frequencies before the amplifier stage. Then a separate amplifier is provided for each driver. In the case of Behringer’s B2031A, there is 150 watts for the woofer and 75 watts for the tweeter.
This approach allows the designer to tailor each amplifier design to suit the specific driver in question. Amplifier/driver interaction is one of the more complicated things in audio reproduction and optimization here can bring big performance improvements. With the amps right in the cabinets there’s effectively no speaker leads to further complicate the amp/driver relationship.