The 36-year-old midfielder will leave the Roar after seven campaigns, three titles and two Johnny Warren medals, having not been offered a new contract for next season.
Broich made the definitive call on his future after talking with Aloisi, who said he would not know what he could offer the former German international until salary-cap calculations were done at the end of the season.
Broich had been unsure if he wanted to play on until two weeks ago, when he first informed the club of his intent.
There is scope for A-League teams to pay up to $200,000 outside the salary cap, as part of a 'loyalty player allowance', but it operates on a sliding scale and it's understood the Roar have used up almost all of it on other players.
Aloisi said it would have been easy for Brisbane to keep Broich, and better for the competition, if that allowance was increased, echoing recent calls from Ange Postecoglou for the cap to be removed.
"The salary cap is that complicated for us to explain to all the supporters; people don't understand - they just go 'why can't you keep Thomas Broich?'," he told AAP.
"It's not as simple as that. I would have loved to.
"It's like Roma with Francesco Totti - you want your legends to be able to stay at their club for the rest of their lives.
"We've been put in a position where we can't keep him, virtually. I don't really agree with it, because this is what can happen."
Broich is believed to be eyeing a shift to Asia, and his move to apply for Australian citizenship could make that easier.
It is hard to imagine him wanting to play for another A-League side, given the depth of his love for the Roar, the club where he rekindled his passion for football in their golden era.
Aloisi said the door was open for Broich to return to the club in a coaching capacity at any time in the future.
He also said the best way for upset supporters to channel their emotion - instead of being angry at the club - was to pack the stands in what could be one of Broich's final matches at Suncorp Stadium, Friday night's elimination final against Western Sydney Wanderers.
"I'm hoping it's not. I'm hoping we play a grand final - but I hope there's a big crowd to see him play because what he's achieved at this football club and the A-League has been phenomenal," Aloisi said.