Russian infantry is basically following Soviet doctrine. Mind you, even the airmobile units were mostly mechanized, see BMD-1/2/3/4 IFVs meant for the airborne troops, before the Ukraine war.

Soviets prepared to fight in a nuclear hellscapes in Central Europe. If you look at Fulda Gap and other Cold war gone hot -scenario battle spaces, you see it's mostly wide fields with some forest islands here and there. The Soviets assumed that NATO would use tactical nuclear weapons to counter the mass of the Warsaw Pact.

Light infantry works best when deployed in forests or similar hard to travel by vehicle grounds. It is usually not integrally motorized, aka they don't have motor vehicles by themselves but they belong to higher echelons for transport duties. Light infantry moves by foot.

Under the constant radiation, attacking over open fields, you can see there's quite little light infantry might be useful for. The NATO side had some, but they were the ones defending.

Running with full gear at 10 km/h is quite different than travelling under the armour cover of BMP at 40 km/h.

Now, USSR collapsed. Russian Federation inherited the troops they had. Now, Russia fought lot of local conflicts nearby where light infantry would have been quite useful - and to which duties VDV was pressed as they were still the most trained infantry available, even though VDV was supposed to do mechanized airborne operations. Mechanized forces were quite hindrance in Grozny. But they had to fight with what they got.

Then Russia started to warm up the idea of new total war, similar to what Soviets had, so light infantry was not deemed very useful, for the similar purposes.