It because the dna:rna hybrid need to be cleaved off and replaced by DNA, if the complex was DNA:DNA then the replication machinery cannot distinguish if it is a primer or replicated DNA hence it would much easier to have a DNA:RNA hybrid which the cells would recognize as a priming event and remove it.

Very thought-provoking question. It has been discussed before on RG:

https://www.researchgate.net/post/Why_we_use_RNA_primer_instead_of_DNA_primers_in_the_DNA_replication

The replicative DNA polymerase can't make primers because it requires a 3'OH group to attach deoxyribonucleotides to. This much is clear. But why isn't there a priming DNA polymerase that can do this instead of a priming RNA polymerase? Then there would be no need to eventually replace the RNA primer with DNA.

Is there a biological reason why it would be disadvantageous for there to be a priming DNA polymerase in the cell? In the previous thread on this topic, Adrian Filip pointed out that there are DNA polymerases known that can initiate DNA synthesis in the absence of primers. He also suggested that a DNA polymerase capable of priming might initiate DNA replication inappropriately in some situations.

Your claim that there is no enzyme able to produce a DNA primer is not quite correct. See for example Gill et al, 2014. Nucleic Acids Res. 42, 3707-3719. A highly divergent archaeo-eukaryotic primase from the Thermococcus nautilus plasmid, pTN2.