Why was I told I cannot have LASIK or any similar surgical procedure because I have mild keratoconus but could have an intraocular lens implanted?

Keratoconus is a condition that can be made much worse with LASIK and thus should be avoided by those who have it. There are several remaining options for you. I know that you know about spectacles and contact lenses, and I would suggest that these are the safest and easiest solutions. You mentioned clear lens exchange, where the human lens of the eye is removed and replaced with an artificial lens, and this is an option. However, in a person of your age, presbyopia (difficulty with near vision) will be an issue even with the presbyopia-correcting lenses. Additionally, the rate of retinal detachment goes up in nearsighted people who undergo lens-replacement surgery. You should also research the option of placement of a lens inside your eye called the ICL, which can be done without removal of the human crystalline lens. There is a treatment for keratoconus that is currently undergoing research around the world that might (repeat might) make your cornea stronger and possibly allow for LASIK in the not-too-distant future. This procedure uses riboflavin and UV light to strengthen the cornea. It might be wise to wait for this treatment to be fully developed prior to making any decisions. I highly suggest that you see an ophthalmologist in your area who specializes in all aspects of refractive surgery and learn more about these many options.