Single-dish telescopes have advantages over interferometers in a few areas; existing answers have touched on some of them. Collecting area is extremely important, as Rob Jeffries mentioned, and you need extremely large arrays to compensate for this. Granted, such arrays are certainly possible (ignoring the fairly sizable cost cost), as demonstrated by the coming Square Kilometer Array in 2027, which will have a collecting area of ~1 km. On the other hand, the SKA is in many ways the exception, not the rule, collecting area included.
Another advantage of single-dish setups arises when investigating large-scale structures. An interferometer's upper limit to its spatial frequency depends on the shortest baseline between any two dishes. Even in its most compact configuration, the Very Large Array's minimum baseline is 35 meters. If you want to quickly map large areas of the sky - important for large, extended sources - you want a single-dish telescope. In cases when you require both large-scale and small-scale spatial sensitivity, a combination of an interferometer and a single-dish may be warranted.
Let's say you want to swap out receivers, or upgrade your instrument for a specialized purpose. In that scenario, it's much more convenient to just have one dish to deal with. It would be much, much simpler to install a new receiver in one dish instead of dozens. Similarly, an interferometer won't be able to easily shift between configurations, which gives an advantage when it comes to scheduling - particularly in an era when radio telescopes are often massively oversubscribed.
As a final note, from a spatial perspective, observations of point sources - pulsars, FRBs, radio transients, etc. - can be done just as easily with single-dish telescopes - which, again, usually have larger collecting areas.