Subleases: Landlord Refuses to Allow Subletting of Apartment

My question involves landlord-tenant law in the State of: Texas

I have taken an apartment for 12 month lease in Texas which started from April 2012 and ends by March 2013. Due to job relocation, i have to move out of this apartment by October., When i checked with apartment manager for subletting or to transfer the lease to my friend who is willing to help me to avoid lease breakage fee, Apartment manager refuse to subletting or to transfer the lease for the reason that apartment has many vacancies. By subletting or transferring the lease, apartment manager complains that he will lose business.

My question is

1) is it legal to refuse subletting or lease transfer for the reason that apartment has more vacancies, even though the person who is going to sublet or take over the lease is brought by me ?

2) What are the reasons with which the landlords can refuse to sublet or transfer the lease ? I m really not sure why i should pay reletting fee even if i bring some one who is ready to take the lease.

Please help me