Annie, just for once I am going to disagree with you. Many people buy clothes and keep them, even though they know that some of them will never be worn.
By taking on clearing your wardrobe for Lent, you are imposing a personal discipline on yourself, if it was not Lent you probably wouldn't be undertaking the clear out. Hopefully when Easter comes you will have also have thought through your attitude to clothes, why you constantly buy them, how it is a statement about you will have made good resolutions to limit your future clothes purchasing to what clothes you need, not what clothes you want.
If the discarded clothes go to charity shops and not to the tip and if you have reformed your attitude to clothes, you are making a contribution towards reducing environmental pollution and global warming.
The purpose of Lenten actions, was always to act as a lesson in personal self-discipline and self-denial, to help us be in more controlled and thoughtful in our actions afterwards and while they have a religious significance for some. Most people, whether they are religious or not will benefit from setting a side a month of the year when they accustom themselves to being self disciplined by denying themselves something they enjoy.
Look at the success of dry Januarys and Vegan Februarys.