…injured something in my lower body?
…have an explicit restriction from my doctor?
…don’t have legs?
…<any other reason>?
But I cycle / run / play soccer?
Ultimately, you are an adult – You can do whatever you want, and you don’t need r/Fitness‘s permission. But skipping strength training for the largest group of muscles in your body is not a good idea, and endurance based exercises are not an adequate substitute for resistance training.