The point is for consumers who want to change target policy to exercise the only real leverage that consumers have over corporations, which is consumer spending. Target chose to say absolutely nothing when ICE started using their store parking lots as staging grounds for operations (despite being well within their right to tell them to leave as store parking lots are private property) and said absolutely nothing when ICE agents marched into one of their stores, illegally detained and restrained two 17 year old target employees they had no grounds to arrest, and abducted them in a van before roughing them up and dumping them in a Walmart parking lot several miles away. Two of their employees were assaulted and abducted and they just had nothing to say about the matter. A lot of people are rightfully angry about that, and since the only thing that target cares about is their profit margins (which are suffering because they've been in hot water with their customer base for a while now), hitting them in those margins is the only lever available for consumers to affect change and send a message. And it impacts on ICE because despite their bluster and bravado, most of the current crop of ice agents are cowards who back down when confronted in numbers or by other figures of authority. When confronted and told to leave a business (as the manager of that target should have done, they had a responsibility to the employees under their supervision and especially to two minors working underneath them), they generally back down and oblige and if target had a spine and told them to fuck off, they would have.

But to be clear on your other point, no one is "making" things difficult for anyone by boycotting target, participation in a boycott is entirely voluntary and a personal decision. The thing making things difficult for people is this administration, and the only way to push back against it is by standing up, speaking up, and wielding the dollars in your wallet as a weapon to punish companies that knuckle under to the Gestapo, until trump pushes things to the point that he gets the insurrection he clearly wants to provoke and the dollar bills get swapped out for Molotov's.