AI - Merger Arb

In a cash-for-stock acquisition, the merger-arb manager may choose to buy just the
target company (T), expecting it to increase in value once the acquisition is completed.

In a stock-for-stock deal, the fund manager typically buys T and sells the acquiring
company (A) in the same ratio as the offer, hoping to earn the spread on successful
deal completion.

Why the difference wrt long and short positions in both the alternatives?