https://en.m.wikipedia.org/wiki/Opium_production_in_

Soviet period (1979–1989) Edit After a Soviet-backed left-wing government in Afghanistan failed to gain popular support, the Soviets decided to invade. A number of resistance leaders concentrated on increasing opium production in their regions to finance their operations, regardless of its haram Islamic status, in particular Gulbuddin Hekmatyar, Mullah Nasim Akhundzada, and Ismat Muslim. The production was doubled to 575 metric tons between 1982 and 1983.[15][16] (At this time the United States was pursuing an "arms-length" supporting strategy of the Mujahideen, the main purpose of which was to cripple the Soviet Union slowly into withdrawal through attrition rather than effect a quick and decisive overthrow.) Hekmatyar, the leading recipient of aid from the CIA and Pakistan, developed at least six heroin refineries in Koh-i-Sultan in southwestern Pakistan, while other warlords were content to sell raw opium. Nasim Akhundzada, who controlled the traditional poppy growing region of northern Helmand, issued quotas for opium production, which he was even rumoured to enforce with torture and extreme violence. To maximise control of trafficking, Nasim maintained an office in Zahidan, Iran.[17]

Its bullshit to paint an invasion as aid. This is what imperialist do.

The soviets invaded afaganistan for the same reasons as the us did later and Briton did before.

To protect their borders from afar,

To create and protect trade deal favorable to their country,

To spread their ideology.

And by the way I read a book about the history of afaganistan called: Games Without Rules: The Often Interrupted History of Afghanistan.

It outlined how the three main invasion of Afghanistan all followed the same basic lines, motivations and results. They devastated Afghanistan and created a situation where they would be invaded again.