There are 2 big reasons
1.Most of them are attracted to females
A study have found that 73%-81% of male-to-female transgendered “females” are still sexually attracted to females.
A survey of roughly 3000 American trans women showed that at least 60% were attracted to women
In this survey trans women respondents 27% answered gay, lesbian, or same-gender-loving, 20% answered bisexual, 19% heterosexual, 16% pansexual, 6% answered asexual, 6% queer, and 6% did not answer
2.Moreover, only 25%-30% of transgender people having undergone gender re-assignment have had any kind of gender-confirming surgery, meaning that more than two-thirds of male-to-female transgendered “females” using women’s public facilities will still have their male genitals intact