Many people have difficulty changing from English to western, especially when it comes to contact.
To me, the most challenging difference between English and western riding is the difference in contact. I switched from English to western and had to learn to give up the direct contact on the mouth - it took me almost two years to break the habit and learn to let go of my horse. For people switching from western to English, the problem will be learning to ride with contact so that the horse can rely on it and balance on steady pressure.
Contact is contact, whether it is an ounce of contact in each hand, a pound of contact or five pounds (and by the way, riding on a loose rein is not riding ‘off contact’ because the horse can still feel your hands and any movement you make, even with slack in the reins). A horse that is ridden on direct contact learns to rely on the contact in part for his balance, just like when you hold a horse’s foot up to work on it - he should not be leaning on you, but he can rely on your contact to help him balance on three feet. So a horse that becomes accustomed to riding on direct contact will often search for the contact and throwing the reins away can be a lot like suddenly dropping out from under a horse’s leg without warning and letting his foot slam to the ground. He can regain his balance, but it would be nice if you gave him some warning before you dropped his foot!
English horses come to rely on contact for balance. It is just a matter of what the horse is used to.
To simplify, English horses balance on the contact and are reliant on the rider to hold the desired frame, while western horses are required to hold themselves in the frame on a loose rein (self-carriage). English horses go ‘on the bit’ (searching out contact and stretching into the bridle) while western horses come off of the pressure from the bit. Western horses learn that if they hold themselves in the desired frame or give to bit pressure, they will find a release and that is known as coming off the bit or seeking out slack. English horses come to rely on the contact for balance.
For both English and western horses, the release of pressure is always the reward, but that release can be relative. You can still give a release of pressure when riding on contact without throwing the reins away. For example, as you ask for more collection you will increase the contact with rhythmic alternating rein pressure; when the horse comes into the frame you want you can soften your hands and thus contact without going to a loose rein. It is still a release and still a reward.
I like for all the horses I ride and train, whether English or western, to be ridden both on contact and on a loose rein in every training session. I also like to ride them both in a natural, long and low frame and at various degrees of collection in each session. There’s no reason why a horse can’t do it all if the rider can adjust. I don’t think riding on contact or on a loose rein is better or right or wrong; it just depends on what you are doing and the style of training. A well-trained horse and a rider with soft and educated hands should be able to do it all.
