# Why the author is quite loose when controlling in control variables for exchange rate regression?

I read a paper from (Han 2020) and from his equation (4)

Δ s i , t + h = α i + β 1 x j , t + β 2 Δ π i , t + h + ε i , t + h , t = 1 , 2 , ⋯ , T − h

where xj,t is the change in Baltic Dry Index, Δπi,t is the inflation differential, and Δsi,t+h is the change in exchange rate.

However, I saw that the exchange rate also be affected by interest rates, confidence, the current account on balance of payments, economic growth and relative inflation rates. So why the paper here did not account for these control variables?