Why is it difficult to get the end-point of a titration with hydrochloric acid and sodium hydroxide when only a single titration is carried out?
I don't think it is especially difficult. However, your measurement may not be very reliable.
This goes back to the old requirements for measurement: (i) accuracy, i.e. your measurement approaching the true value; and (ii) precision, the repeatability of your measurement.
Now the one measurement might be reasonably accurate, but would you stake your reputation on the one reading? Multiple measurements allow you to quote an error value, a check on the precision of your measurements.
For a simple acid base titration as shown:
you should be able to get results that are both highly precise and accurate.