With out knowing and seeing what the condition of the vehicle or what and how the work was done I can only offer some suggestions
What is the year and mileage of the vehicle?
When was the last time the brake fluid was changed?
If it has been more than several years… suggest a fluid flush of the entire system.
As to the flexible brake hoses… how old are they?
There may be internal issues, might all look good externally but internally is another story.
What condition are the rotors in? Just surface rust is rarely an issue and clears up very quickly
I assume you removed the calipers when doing the ball joints.
Possible you may have dislodged some debris inside the caliper(s) which may be hanging them up.
Did you clean and re-grease the slide pins?
Make sure the pads move freely on the bracket?
Make sure the pad surfaces are not glazed or cracked.
There really shouldn’t be any reason that doing ball joints should affect the brakes unless the brakes had a border line issue.
In which case you’ll need to start looking specifically at the brakes and perhaps doing a full service on them.