Why aren't there 2 products formed?
A lone pair on the ring oxygen forces Chlorine leave. The anomeric carbon in the resulting oxocarbenium ion is sp 2 hybridized, so that part of the molecule is planar. (An oxocarbenium ion has a positive charge that is shared by a carbon
and an oxygen.)

When the alcohol approaches from the top of the plane, equitorial isomer is forrmed. Similarly if alcohol apporoches from bottom of sp2 hybridised oxo carbenium ion , then ,axial isomer is formed .So the given chloro compound should give two isomers (as shown in figure below 2&amp; 3)..

Which is the major product ?

Substituents on a cyclohexane ring prefer the equatorial position to relieve steric strain. cyclohexane ring in chair form with substituent in equitorial position ring-flipps to chair in which the substituent is axial.



When an endocyclic heteroatom ( oxygen, nitrogen, or sulfur) is  at a position adjacent to the methoxyoxy group,the hetroatom substituent now prefers the axial orientation (despite of the associated steric strain).The equilibrium preference of most such compounds for the alpha-isomer is referred to as the anomeric effect.



Such behavior is explained as


In α-methyl glucoside, the non bonding HOMO with a pair of electrons on the ring oxygen is antiperiplanar to the antibonding LUMO of C-O bond in methoxy group. This allows hyperconjugation between them and thus by stabilizing the α-form. 
In axial position,such interactions are possible.Whereas, in equitorial the methoxy group is at equatorial position and cannot involve in hyperconjugation since it is not antiperiplanar to the lone pair on ring oxygen. Therefore  equitorial isomer is less stable than the axial isomer.




Other Explanations:


The  dipole interactions of the two ether functions are  in the equatorial conformer are nearly parallel;while, in the axial conformer these dipoles are oriented in opposite directions. 




image source :https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/carbhyd2.htm#anomr


Electrostatic Repulsion: Decreased electrostatic interactions are favored



All the above combination of factors result in equitorial isomer being less stable than the axial isomer.

Referance

https://www.scripps.edu/baran/images/grpmtgpdf/Krawczuk_Nov_05.pdf

Organic Chemistry ,SEVENTH EDITION , Paula Yurkanis Bruice