A land trust may not be willing to accept the easement because of the size, location, or characteristics of the property. The property may have no special or unusual characteristics worth preserving, except that you are not putting another house on it. If it appears that you are rather trying to get away with something on your taxes, or even simply that there is nothing particularly unusual about your property or its setting, a land trust will not be willing to accept the easement.
Land trusts have limited resources.
They must be careful in accepting the responsibility and costs of ongoing monitoring and enforcement of easements on many small properties and properties of no special public interest. They do not wish to hold easements on what are essentially people's backyards. If land trusts appear to support questionable tax dodges, their general credibility and success will be undermined. Anyway, if there is nothing particularly unusual about your property or its setting, you probably will not receive an income tax deduction from the IRS for your donation, negating the costs you have borne in donating the easement. Land trusts often follow written guidelines that establish eligibility.