Belarus is analytically inseparable from the Russia programme, and its principal interest is as a case study in closing a circumvention route.
Why the measures were aligned
Substantial parts of the Belarus restrictions were introduced or expanded specifically because Belarus represented an obvious route around Russia-related measures: a neighbouring customs union member with integrated rail and road links and its own trading relationships.
The measures were then aligned across the coalition partners, more or less in parallel with the Russia measures, precisely so that the two could not be arbitraged against each other.
What that illustrates
The Belarus programme is a compact demonstration of the central dynamic in this whole subject. Restrictions create an incentive to route around them; routing around them is geographically and commercially predictable; and the response is to extend the restriction to the route.
Each iteration of that cycle pushes the routing further from the target and makes it more expensive, which is the mechanism by which sanctions are actually intended to work.