“The maintenance of sexual reproduction in a highly competitive world has long been one of the major mysteries of biology given that asexual reproduction can reproduce much more quickly as 50% of offspring in sexual reproduction are males, unable to produce offspring themselves.” source: Wikipedia
Put another way, from an evolutionary perspective, sexual reproduction would need to provide an advantage of more than 50% to be maintained as viable in the long term.
Several theories have been proposed. A 2015 hypothesis (from the University of East Anglia, UK) suggests that :
“In the absence of sex, populations accumulate deleterious mutations through a ratcheting effect where each new mutation takes a population closer to extinction. Sexual selection helps to remove those mutations, enabling populations to persist against the threat of extinction.” source: phys.org
There are however many organisms that have maintained extensively successful populations over millions of years apparently asexually, see wikipedia
Observation. This topic needs more detail