The Mongols also did that all the time. You leave the enemy an escape path and then you use pinprick attacks to mow them down as they escape. This way you avoid time consuming siege battles.
Leaving a route to escape is part of Sun Tzu's Art of War.
Leaving some people alive to escape is also a weapon by itself, as these people will show fear among their own army.
To be fair, winter is coming. I think we're going to see a slowdown in Russia's tempo soon.
But maybe not, I can see the merits of pressing their advantage. Even in horribly crappy winter weather.
Winter hardens the ground once again, making vehicles passable. You also lose a lot of foliage, putting defenders at risk. It makes forests open ground which advantages the force with greater fire power.
Unrelated, additional news.
Iskander strikes with cluster munitions at Dnipropetrovsk air base. One MiG-29 fighter taken out. Up to 15 engineering and technical staff allegedly killed. Infrastructure damaged.
Russian flag raised over Kopanka at the Kharkhiv region.
Olgovsky forest completely captured. This salient, the Russians did not allow the Ukrainians to escape, no escape route was left. Compared to other areas in the front, the Russians in Kursk are more prone to kill their opponents, although prisoners are still taken.
Boom. Big explosion at the Kurakhovsky Thermal Power Plant, like the arrival of a huge FAB. The city is now in the midst of battle and encirclement.
M113 gets Krasnopoled near Kurakhovo.
Maxxpro burning after hit by FPV in Toretsk.
Members of the Mad Dogs unit have taken out a Baba Yaga.
Ukrainian T-64BV firing at Russian positions, gets hit by an FPV drone to the rear.
Medvedev visits the tank production plant and mentioned that since the start of the war, production has increased 8 times.
Russians get busy building reinforced concrete shelters in their air bases.
Prince Vandal drone hunts and attacks a Roschel Senator.
British AS-90 155mm SPG found destroyed.
By following a drone, reconnaissance discovers the location of a Ukrainian UAV control point in Kherson, and Russian troops put an ATGM into it. The Kornet-M or 9M133M, has a range of 10km with a thermobaric warhead, and is the weapon most likely used against non tank targets.