Look at the elegant union halls, fancy cars and big salaries for the union bosses. That's where the money goes. I've worked on the management side of 3 strikes while I worked at PacBell. The union strike fund barely offers a crappy bag of groceries to the striking employees. If a union member dares to cross the the line, they can be fined all the money they earn and more. If you live in Southern California, the last thing you need is to go on strike with exorbitant rents and mortgages.
The usual PacBell strategy was to keep the union walking the picket line until the payroll savings exceeded all the increased pay and benefits that they were willing to conceded at the bargaining table. The union members ALWAYS lose. The hourly pay losses will always exceed what the fat cat bosses negotiate at the table. It's a game that keeps the union bosses rolling in money and the members pockets raided to cover political contributions to Democrats.
The secondary benefit accrued at PacBell was more subtle. They figured out how to run the company more efficiently with fewer union people. The strikes give them a chance to test new ideas. The usual consequence is a phaseout of jobs that can be done more efficiently. In the central offices, the wire chiefs take care of fixing stuff that their incompetent subordinates can not or will not fix. Making such fixes during an active contract would be cause for a grievance to be filed.
How does this apply to a grocery strike? The Walmart model of non-union employees that can do those jobs without exorbitant pay and benefits packages. Installation of self-scan checkout machines (we have them in Idaho at Fred Meyer's) to achieve a 4X reduction in cashier costs. Unemployment rates are sufficiently high to provide a large labor pool of folks willing to work for a lower compensation.