subplot() does not include titles from ggtitle()

The following code does not include the text from ggtitle() in each subplot:

library(ggplot2)
library(plotly)

gg1 <- ggplot(data=iris) +
  geom_point(aes(x=Sepal.Length, y=Petal.Length)) +
  ggtitle("PLot 1")
gg2 <- ggplot(data=iris) +
  geom_point(aes(x=Sepal.Length, y=Petal.Width)) +
  ggtitle("PLot 2")

subplot(ggplotly(gg1), ggplotly(gg2), nrows=2)
sessionInfo()

R version 4.0.4 (2021-02-15)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Pop!_OS 21.04

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=es_ES.UTF-8        LC_COLLATE=en_US.UTF-8     LC_MONETARY=es_ES.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=es_ES.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=es_ES.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] plotly_4.10.1.9000 ggplot2_3.4.0     

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.9        plyr_1.8.6        pillar_1.8.1      compiler_4.0.4    tools_4.0.4       digest_0.6.30     viridisLite_0.4.1 jsonlite_1.8.4    evaluate_0.17    
[10] lifecycle_1.0.3   tibble_3.1.8      gtable_0.3.1      pkgconfig_2.0.3   rlang_1.0.6       cli_3.4.1         DBI_1.1.1         rstudioapi_0.13   crosstalk_1.2.0  
[19] yaml_2.3.6        xfun_0.35         fastmap_1.1.0     withr_2.5.0       dplyr_1.0.10      httr_1.4.2        knitr_1.40        generics_0.1.3    vctrs_0.5.1      
[28] htmlwidgets_1.5.4 grid_4.0.4        tidyselect_1.2.0  glue_1.6.2        data.table_1.14.2 R6_2.5.1          fansi_1.0.3       rmarkdown_2.14    pander_0.6.5     
[37] tidyr_1.1.3       purrr_0.3.5       magrittr_2.0.3    scales_1.2.1      htmltools_0.5.3   assertthat_0.2.1  colorspace_2.0-3  labeling_0.4.2    utf8_1.2.2       
[46] lazyeval_0.2.2    munsell_0.5.0    

I get:

Start by running the supplied R example with ggplot2 and plotly, comparing ggplotly(gg1) and ggplotly(gg2) with the combined subplot() output. Inspect the subplot() and ggplotly() entry points to trace how ggtitle() text is handled. Done means each subplot displays its corresponding title in the combined visualization.