He was the only passing option. Maguire's job to stay close to him. What did he do? Sacred of ghost runner, and came into his senses second later after Weghorst had the ball under control, and had all the composure for his next move and string Maguire along like a schoolboy.
Your defense for Maguire failed for that reason. There was no reason for Maguire to leave Weghorst because Burnley have no better option than passing to Weghorst, and by then McTominay already recovered lost ground. Then Maguire continued his series of brain fart by commit his body.
McTominay was running straight at the direction Weghorst was facing. It's a very normal direction to apply pressure. What abnormal was Maguire who was behind Weghorst at this moment charging blindly yet missing both the body and the ball. It's hard to tackle from behind, so why bother, but it's so easy to commit a tactical foul against a tall player. Maguire made the impossible.
Also Weghorst has very few option after he received the pass. He chose a very difficult options to turn on Maguire direction, and surprisingly it was the best outcome.