BigInt and Number conversions

When working with numbers in JavaScript there are two primitive types to choose from - BigInt and Number. One could expect implicit conversion from "smaller" type to "bigger" type which isn't a case in JavaScript.

Expected

When computing some combination of BigInt and Number user could expect implicit cast from Number to BigInt like in below example:

const number = 16n + 32; // DOESN'T WORK
// Expected: Evaluates to 48n

Actual behavior

Expressions operating on both BigInt and Number are throwing an error:

const number = 16n + 32; 
// Throws "TypeError: Cannot mix BigInt and other types, use explicit conversions"

Why explicit conversion is needed in above cases?

Or in other words what is the reason behind this design?

This is documented in the original BigInt proposal: https://github.com/tc39/proposal-bigint/blob/master/README.md#design-goals-or-why-is-this-like-this

When a messy situation comes up, this proposal errs on the side of throwing an exception rather than rely on type coercion and risk giving an imprecise answer.